Keywords

4.1 Introduction

The biosensor is an analytical device that senses biological materials and estimates it by biological signals. These signals are then evaluated and converted into readable form using transduction and electromechanical interpretation. Figure 4.1 represents a model of a biosensor and gives information about its components. There are three major components of a biosensor, namely bioreceptor, transducer, and detector. Their main function is to sense a biological material like immunological molecules, biomolecules, and enzymes.

Fig. 4.1
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Graphical representation of component of biosensor

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Nanomaterials have unique properties; therefore, they can be exploited for the development of sensitive nanobiosensor. The nanomaterial-based sensors are economical, reasonable, robust, and reproducible (Rai et al. 2012). Thus, nanobiosensor is used to determine a biochemical or biological event through a compact probe (Di Giusto et al. 2005; Gullberg et al. 2004; Prasad 2014). At present, it is considered that nanobiosensor technology can revolutionize the health care industry because of applications for human health like monitoring of diabetes, measurement of metabolites, detection of cancer biomarkers, and in forensic medicine, etc. In the victuals industry, nanobiosensor is used for remote sensing of water quality, monitoring the presence of drug residues in food. They can also be used for the detection of pesticides in the environment, heavy metals in river water, and genome analysis of organisms. The nanomaterials like silver, gold, magnetic nanoparticles, carbon nanotubes, and quantum dots have been vigorously investigated for their application as biosensors. Several studies reported that the silver and other metal nanoparticles have significant applications in the field of biolabeling (Kulesza et al. 2009), drug delivery system (Lv et al. 2009; Marcato and Durán 2008), filters, and as antimicrobial drugs (Durán et al. 2010; Rai et al. 2009) and sensors (Baruah and Dutta 2009).

4.2 Nanobiosensor and Their Properties: Fusion of Nanotechnology with Biosensor

Nanotechnology has contributed a lot in the field of biosensor development due to its unique electronic, magnetic, and optical properties of the nanomaterials used. The special characteristics like submicron size and large surface area to volume ratio enhance the sensitivity of the nanosensor for the analyte. Nanomaterials are considered environmentally sustainable and thus can be utilized in sensing technology. Nanobiosensor is defined as a device that is used to detect analyte quantitatively with the help of a biologically active element attached to a suitable nanostructured transducer (Fan et al. 2008; Velasco-Garcia 2009; You et al. 2009). Nanobiosensor is a modified version which has biologically sensitive molecule immobilized onto the surface of the physico-chemical transducer. It is the effort of researchers working in diverse fields like electronics, biologists, material chemist, and physicists (Turner 2000). It is a compact analytical device that has enhanced inherent specificity, quick response time, and reliability. The important property of a biosensor is the specificity and it should be high enough to determine analyte from the rest of the unwanted material. The interaction between the target analyte and sensor should not be affected by physical factors like temperature and pH. Also, the sensor should provide analysis results with precision, accuracy, and linearity without the disturbance of electrical noise. Stability is another important criterion for an ideal nanobiosensor under normal storage conditions. It should be economical, inexpensive, manageable and should be conveniently used by semi-skilled operators (Rai et al. 2012). Although nanobiosensor is still in the developing stage but it has shown promising results in bioanalytical applications and has gained popularity because of its ability to detect ultra-low concentrations of any analyte that are observed to be a potent threat to the living being. It works at the atomic level with great efficiency, and due to its high sensitivity, sometimes it is considered to be an error-prone system (Rai et al. 2012).

The biologically active or recognition element, the transducer, and the detector are three important components to formulate any nanobiosensor. The biological elements used are bioreceptor probes that are highly selective for target analytes like antibodies, nucleic acids, pathogens, and metabolites. Molecular recognition elements include biologically derived materials or bio-mimic components such as receptors, enzymes, nucleic acids, antibodies, molecular imprints, lectins, tissue, microorganisms, and organelles (Razavi and Janfaza 2015; Sharma and Rogers 1994). The working of nanobiosensor starts with the binding of targeted bioanalytes with the bioreceptors and this binding generates a physicochemical signal which is modulated by the receptor. The transducer can be electrochemical, mass, optical, and thermal. The transducer measures changes which occur as a result of heterogeneous reaction at bioreceptor/element and thus acts as a borderline between receptor and detector. It captures and transforms the signal into measurable electrical output. This electrical signal is trapped by the detector component which is further amplified and observed by the microprocessor (Prasad 2014).

In nanobiosensor, the change in the signal like electric potential, current, impedance, intensity, current, and phase of electromagnetic radiation is measured. These variations are analyzed and confirm the presence or absence of bioanalytes. The properties of transducers and biorecognition element determine the sensitivity of a nanobiosensor. The nanostructured materials are located between the biological agents and detector component and thus behave as intermediary phase and this nanomaterial is immobilized on the transducer in order to fabricate a nanobiosensor. Several nanomaterials have been screened for the development of nanobiosensor (Gomes et al. 2015; Sharma and Rogers 1994). The nanostructured materials of different chemical nature are discussed in the next section.

4.2.1 Nanomaterials Used in Biosensing Devices

Recent years have seen tremendous growth in using nanoscale materials for developing electrochemical biosensing devices as the properties of nanomaterials offer an excellent outlook in constructing high performance, novel sensing systems. The nanomaterials are incorporated into the transducer which can send the observable signal to the recorder. Controlling the size and morphology of nanomaterials can enhance the power of detection, sensitivity, and transducing capability to a certain degree (Pak et al. 2001). There are few factors which are kept in mind while selecting a particular kind of nanoscale material.

Materials at the nanoscale level are integrated with highly sensitive electrical and electromechanical properties when engineered with the nanoelectromechanical systems (NEMS). It has enabled the materials to gain complex electrical, mechanical, fluidic, thermal, optical, and magnetic properties. NEMS is a class of devices and as the name suggests, the device is in the nanometer range and thus having novel features like low mass, high mechanical resonance frequencies, more surface-to-volume ratio, and large quantum mechanical effects such as zero-point motion. NEMS and MEMS (microelectromechanical system) devices have resulted in mechanical materials to perform in a much better and sophisticated way as the mechanical property of a material determines its size. MEMS is a mini device with electrical and mechanical components. Using these devices, surface forces like adhesion, cohesive, friction, and viscous drag force can be regulated precisely which helps in biochemical interaction taking part in sensing technology. Incorporating nanomaterials with these devices increases the response to a wide range of stimuli (Bhushan 2007).

Optimizing the optical properties of nanomaterials is also one of the important criteria considered for its selection. Plasmon surface resonance is an interesting feature of nanomaterials which maximizes the optical response of the sensing materials with the incident light. Ionic and charged species are used to excite the surface of sensing materials and cause excitation of the fluidic state of charged particles. Due to this phenomenon, nanoparticles have photonic character and can be used as fluorophores. The refractive index of a medium is a vital property that governs the flow of light through a medium and also affects the surface plasmon resonance. A nanobiosensor is thus able to detect the infinitesimal biological interactions and results in a much better and reliable degree of estimation. So, for the implementation of nanomaterials, they are to be optimized for their performance and effect to be used in biosensing devices as per the required goal (Haes and Van Duyne 2002; Kelly et al. 2003). Tailoring of physical/chemical properties like shape, size, structure, and composition of nanomaterials is done to alter the specific absorptive, emissive, and light-scattering features. Various nanostructured materials have been modified and utilized with specific forms such as 0D (quantum dots, nanoparticles), 1D (nanowires or carbon nanotubes), or 2D (metallic platelets or graphene sheets) orientation that reflects in their final properties (Pandit et al. 2016). These nanomaterials are described below.

4.2.1.1 Metallic Nanoparticles

Due to their microscopic size, high surface to volume ratio, electrical and optical properties, metallic nanoparticles have been a huge success in diverse fields. They have been exploited in bioanalytical applications for the development of biosensors, diagnostics, imaging, drug delivery, and therapy. Among metal NPs (1–100 nm in size), gold nanoparticles (GNPs) have been widely employed for such applications. They have a large surface area, strong adsorption ability, scattering properties, and facile conjugation to various biomolecules and are considered as nontoxic, biocompatible, and inert core nanomaterials. Gold NPs are being extensively used for the detection of various analytes by fabricating it into immunoassays, diagnostics, and biosensors. They can act as nanocarriers for the delivery of drugs, DNA, and genes in the therapy of cancer and other diseases (Kim et al. 2002; Park et al. 2013). After GNPs, magnetic NPs (MNPs) are the second most common NPs which have been used in the development of nanobiosensor and detection of analytes such as proteins, enzymes, DNA, mRNA, drugs, metabolites, pathogens, and tumor cells. The MNPs are being extensively used by industries to develop diagnostic magnetic resonance (DMR) technology and nuclear magnetic resonance detector (μNMR) which can detect a sensitive analyte in microliter volumes (Sahoo et al. 2017). Silver nanoparticles (AgNPs) are also very commonly synthesized and considered to be a noble metal having attractive physicochemical properties including the surface plasmon resonance and large effective scattering cross-section of individual silver nanoparticles. They have been used in diverse applications effectively including the detection of biological macromolecules. Hydrophobic Ag–Au composite nanoparticles have been observed to show strong adsorption and good electrical conducting properties and thus are being used in biosensing devices (Link et al. 1999; Rai et al. 2012).

4.2.1.2 Carbon Nanotubes (CNTs)

Since the discovery of carbon nanotubes (CNTs) in the 90s, its application has been heavily investigated in biosensing devices. The first CNT-based nanosensor was fabricated in 2003 by Wang and Musameh (2003) and Yun et al. (2009). CNTs are an exciting, one-dimensional, and a new form of carbon-based nanostructured material that has already been exploited in many fields like diagnostics, tissue engineering, cell tracking and labeling, and delivery of drugs and biomolecules (Pandit et al. 2016). CNTs are cylindrical in shape and consist of one, two, or several concentric graphene sheets seamlessly wrapped into a tube, capped by fullerenic hemisphere. There are two main types of CNTs—single-walled and multi-walled. CNTs have gained attention due to their unique properties such as structure-dependent electronic and mechanical properties, high thermal conductivity, excellent biocompatibility, high chemical stability, extraordinary electrocatalytic activity, very low surface fouling, low overvoltage, and high surface to volume ratio (Pandit et al. 2016). The surface of CNTs can be modified by adsorbing biomolecules such as protein, DNA, etc., electrostatically or it can be attached to the functional group present on the CNTs. CNT-based nano biosensor has been used in the diagnosis of analytes in healthcare, industries, environmental monitoring, and food quality analysis.

4.2.1.3 Graphene

Graphene is made up of a thin layer of sp2-hybridized carbon. Due to its exquisite properties such as electron transfer ability, high mechanical strength, high thermal conductivity, tunable optical properties, tunable bandgap, high elasticity, very high room temperature electron mobility, and demonstration of the room temperature quantum Hall effect, graphene is becoming more popular than other nanomaterials in bioanalytical and bioimaging applications. Their superior performance facilitates them to be widely used in electrochemical, impedance, fluorescence, and electrochemiluminescence biosensors for the detection of a wide range of analytes such as glucose, cytochrome c, NADH, hemoglobin, cholesterol, ascorbic acid, dopamine, uric acid, hydrogen peroxide, horseradish peroxidase, catechol, DNA, heavy metal ions, and gases. They also have low production costs and minimize harmful environmental effects (Pandikumar et al. 2014).

4.2.1.4 Quantum Dots (QDs)

QDs have unique spectral properties and thus recently, they have been exploited as a new generation of fluorophores in bioimaging and biosensing. They are nanostructured materials with size ranging from 1 to 10 nm. QDs have unique optical properties of broad excitation, narrow size-tunable emission spectra, high quantum yield and molar extinction coefficients, high photochemical stability, and negligible photobleaching (Androvitsaneas et al. 2016). Optical biosensors have been developed using QDs (inorganic nanocrystals) as nanomaterials exclusively for the detection of ions, organic compounds, pharmaceutical analytes, and biomolecules such as nucleic acids, proteins, amino acids, enzymes, carbohydrates, and neurotransmitters (Androvitsaneas et al. 2016; Bakalova et al. 2004; Bulovic et al. 2004).

4.2.1.5 Nanowires and Nanorods

Nanowires are semi-conductor nano-structured materials having unique optical and electronic properties with size ranging from several tens to over 100 μm length and are sensitive enough to detect the binding events of small molecules, peptide nucleic acid (PNA)–DNA as well as DNA–DNA hybridization. Due to their structure, nanowires also show distinctive absorption and photocurrent characteristics. Nanowire-based nanobiosensor shows the sensing procedure when there is a change in charge density (inducing the change in the electric field on the nanowire surface) upon binding of biomolecules (negatively charged molecules bind to the n-type field-effect transistor) (Ambhorkar et al. 2018; Panpradist and Lai 2016).

Nanorods are nanoscale objects having dimensions range of 1–100 nm. Due to their optoelectronic properties, they are gaining momentum in developing different designs of nanosensors. Gold nanorods (GNRs) are considered an excellent candidate to be used in sensing devices as the absorbance band changes with the refractive index of local material and thus allows extremely accurate sensing. GNRs were used in detecting target sequences of infecting agents of many dangerous diseases, for example, an HIV-1 (He et al. 2008).

4.3 Types of Nanobiosensor

Nanobiosensor has been classified broadly based on bioreceptor used and the types of the transducer. Different biomolecules are being immobilized on the surface of the transducer as a bioreceptor which can be divided into several classes such as enzymatic biosensor, DNA/RNA biosensor, immunosensor, aptasensor, and microbial biosensor (Razavi and Janfaza 2015). The classification can also be done based on transducer used for sensing such as electrochemical, optical, etc.

4.3.1 Classification Based on Bioreceptor

4.3.1.1 Enzymatic Biosensor

Enzymes that are specific for an analyte to convert it into a product can be immobilized with a suitable transducer. Figure 4.2 represents a schematic diagram of an enzymatic biosensor. Enzymatic biosensor measures the activity of enzymes selectively upon interaction with a specific target and generates a biological signal proportional to the target analyte concentration. These biosensors have been used to detect analytes at nanoscale level especially with an electrochemical transducer. There is a heterogeneous electron transfer occurring between the electrode and the protein redox center which governs the performance of this biosensor. The enzymatic biosensor is the most common nanobiosensor developed till now, for e.g., glucose nanobiosensor for the rapid self-diagnosis of blood glucose levels (Lad et al. 2008; Trojanowicz 2002; Wang et al. 2014).

Fig. 4.2
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Schematic representation of the enzymatic biosensor. Reprinted with permission from Kurbanoglu et al. (2017). © 2018, Springer

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4.3.1.2 Oligonucleotide (DNA/RNA) Biosensor

Oligonucleotide biosensors are diagnostic devices that consist of a probe (single-stranded DNA/RNA) that is in association with or integrated within a transducer or transducing micro nanosystem as shown in Fig. 4.3. The transducer employed for achieving high sensitivity can be electrochemical, optical, thermometric, piezoelectric, magnetic, or micromechanical (del Valle and Bonanni 2014). DNA based biosensor is a current approach and researchers are trying to develop DNA biosensors for low-cost detection of specific DNA sequences in human, viral, and bacterial nucleic acids, several attempts have been made to increase sensitivity and selectivity of the sensor (Zhao et al. 2014). Nanomaterials play an important role in DNA biosensor, i.e. it is used as a substrate for DNA attachment as well as amplifies the signal for hybridization, an enhanced amount of DNA immobilization occurs on nanomaterial and another advantage is that DNA maintains its biological activity. Nanoparticles like gold, cadmium sulfide, nanowires like silicon, nanotubes like carbon nanotubes, etc., are being employed for DNA biosensor (Sheehan and Whitman 2005; Shi et al. 2013). Electrochemical based DNA biosensor has been fabricated to detect genetic mutations. It can also be applied for gene analysis, detection of genetic disorders, clinical diagnostics, tissue matching, and forensic investigation (Odenthal and Gooding 2007).

Fig. 4.3
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General design of DNA biosensor. Reproduced from Asal et al. (2018). © 2018 (CC BY 4.0)

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4.3.1.3 Immunosensor

Immunosensors are based on immobilized antibodies as a biological recognition element that is highly specific and has been widely applied in clinical analysis; a typical immunosensor is shown in Fig. 4.4. These have been generally used to detect disease at a molecular level. Microorganisms like Escherichia coli, Salmonella, Staphylococcus aureus, pesticides, herbicides, etc., have been detected with high accuracy (Shirale et al. 2010). Viral antigens of tumor have been detected upon the interaction of antigen with the antibody receptor by measuring the response in conductivity across the immunosensor surface and change in the resistance (Bahadır and Sezgintürk 2015; Cruz et al. 2002; Shirale et al. 2010).

Fig. 4.4
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Schematic diagram of immunosensor binding configuration. (a) Sandwich structure formation, (b) competitive style immunoassays and (c) extended sandwich structure formation (d) sandwich structure formation on a (micro-nanoparticle) surface. Reproduced from Asal et al. (2018). © 2018, (CC BY 4.0)

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4.3.1.4 Aptamer Biosensor

Aptamers are a new class of oligonucleotide/nucleic acid recognition elements as they have high selectivity and affinity towards their target. These are single-stranded nucleic acid or peptide molecules having a size less than 25 kDa with a natural or synthetic origin. They can be used for the development of a sensor for DNAs, proteins, and small molecules. The nucleic acid molecules are selected by an in vitro selection process called SELEX (Systematic Evolution of Ligands by Exponential Enrichment) from random sequence libraries (Radko et al. 2007; Sassolas et al. 2009). They have been developed widely for diagnostic applications, e.g. detection of a wide range of non-nucleic acid analytes. DNA aptamer biosensor has also been used for the separation or capture of pathogens and small molecules (Nguyen et al. 2009). These biosensors have been created for a variety of targets such as proteins, peptides, small organics, and whole cells. It has been immobilized on a variety of transducers for the detection of proteins (Liu et al. 2011).

4.3.1.5 Microbial Biosensor

Microbial nanobiosensor is an analytical device which comprises nanomaterials as transducer and an immobilized viable or non-viable microorganism or whole cell. This type of nanobiosensor generates a measurable signal proportional to the concentration of analytes (Shin 2011). Several microbial nanobiosensors have been developed for the detection of glucose on the basis of oxygen consumption of the respiratory activity in the microbes (D’souza 2001). Electrochemical and optical techniques have been commonly used for the development of such biosensors. The selectivity of such biosensors can be enhanced by blocking or inhibiting undesired metabolic pathways and transport mechanisms and inducing targeted metabolic activities (Gäberlein et al. 2000).

4.3.2 Classification on the Basis of Transducer

4.3.2.1 Electrochemical

Most of the nanobiosensors developed so far are based on electrochemical detection as they have many advantages over other sensing techniques such as fast response time, highly sensitive, low cost, low-interference characteristics, and compatible with microfabrication technology, small size, economical cost, minimum power requirement, ease of use, and low maintenance (Bertók et al. 2013; Lad et al. 2008). In this technique, biochemical reactions between the nanofabricated biomolecule or biological element and target analyte are being analyzed with the help of electrical means (Chaubey and Malhotra 2002; Cai et al. 2001). It works on the principle of electrochemistry. The readable electrochemical signals are detected during a bio interaction when an electron is consumed or produced and are measured by the electrochemical method (Chaubey and Malhotra 2002). The electrical signals quantitatively correspond with the concentration of analyte present in the sample (Ronkainen et al. 2010). In a study by Sistani et al. (2014), biochemical detection of penicillin was done successfully using penicillinase enzyme immobilized on nanoparticles (Sistani et al. 2014). Electrochemical nanosensors can be categorized into potentiometric, conductometric, amperometric, and impedimetric biosensors according to their working principle.

Potentiometric nanosensor is based on measuring the potential of a system at a working electrode with respect to a sensitive and accurate reference electrode under zero current flow (Koncki et al. 2000). This potential is generated by converting the biorecognition process and obtaining analytical information of a system (Dzyadevych et al. 2004). The potential signal is generated due to the accumulation of ions at ion-selective electrodes and ion-sensitive field-effect transistors at equilibrium (Koncki et al. 2000). It has been well-established and utilized in the biomedical field, in the detection of various analytes such as antibiotics, preservatives, heavy metals, and pesticides in agricultural and food industries (Durán and Marcato 2013).

Conductometric nanosensor measures change in conductivity of the solution once the interaction of target and immobilized analyte is achieved. The principle is based on a change occurring in electrical resistance between two parallel electrodes during a biochemical reaction (Mikkelsen and Rechnitz 1989; Muhammad-Tahir and Alocilja 2003).

Amperometric nanosensor allows subsequent measurement of current produced by oxidation or reduction of an electroactive species in an electrochemical reaction. They have been mostly used in medical devices and offer many advantages over other electrochemical sensors as they are highly sensitive, fast, precise, accurate, and economical and have a wide linear range (Wang 1999). It has been used in fields of health and diagnostics like development of ATP sensor (Kueng et al. 2004) and beta-HCG sensor (Santandreu et al. 1999) for pregnancy test, in environmental and agriculture like detection of organophosphates, ractopamine, sulfonamides, and hydrogen peroxide (Lin et al. 2013; Xu et al. 2013; Yan et al. 2013).

Impedimetric nanosensors have not been used frequently as compared to other electrochemical sensors. It basically measures the electrical impedance of a particular biological system and gives analytical information about that system (Chuang et al. 2011; Huang et al. 2008).

4.3.2.2 Optical

Optical nanobiosensor measures the change in optical signal and this change is recorded in resonant frequency after the interaction between the analyte and a resonator which oscillates a light within a cavity (Vo-Dinh 2005). They are a powerful and versatile detection tool and highly sensitive to biomolecular targets and provide a quick response. They are insensitive to electromagnetic interference. Optical methods include surface plasmon resonance (SPR), localized surface plasmon resonance (LSPR), surface-enhanced Raman scattering, fluorescence spectroscopy, colorimetric spectroscopy, total internal reflectance, light rotation, and polarization (Borisov and Wolfbeis 2008).

Surface plasmon resonance (SPR) is an optical sensing technique that involves the interaction of light with the electrons of metal and hence causes transfer of energy to electrons present at the surface of the metal (Haes and Duyne 2004). SPR based biosensors have been successfully utilized in fundamental biological studies, drug discovery, health science research, and clinical diagnosis and can detect a wide range of analytes such as proteins, small molecules, antibody–antigen, DNA and RNA hybridization, concanavalin A, antibiotics, mycotoxins, and pathogen like E. coli (Liedberg et al. 1983).

In localized surface plasmon resonance (LSPR), a local oscillation occurs in the close proximity of metallic nanoparticles (MNPs). Light interacting with the MNPs are much smaller than the incident wavelength. This technique has been utilized successfully due to its label-free method as they do not require labeling of the target molecule with any kind of reagent and high sensitivity favors the method (Jia et al. 2012).

Fluorescence biosensor measures change in fluorescence which recognizes and gives information on the presence, activity, or conformation of a given target specifically and quantitatively and hence provides the dynamic molecular behavior. They are known to have high sensitivity, quick response and have the ability to achieve high spatial resolution through spectroscopic and imaging methods. Detection of some analytes such as nitrite, reactive oxygen species, pathogenic bacteria such as S. aureus, V. parahaemolyticus, S. typhimurium, and E. coli have been done by this technique (Chen et al. 2016; Dasary et al. 2008; Hu et al. 2014; Wu et al. 2014).

Colorimetric biosensor measures the change in absorption when a reaction proceeds and forms a colored product. It has been applied to a diverse field such as environmental detection of the toxic metal, clinical diagnosis of analytes, such as glucose, cancer biomarkers, and viruses (Cao et al. 2014; Chen et al. 2014; Sener et al. 2014; Zhang et al. 2014).

4.3.2.3 Piezoelectric

The piezoelectric sensor measures the change in the resonant frequency of piezoelectric quartz which oscillates under the effect of electric field and this frequency is proportional to surface adsorbed mass which changes due to absorption or desorption of molecules from the surface of the quartz. The crystals contain biorecognition element on its surface which selectively binds with the target and causes a change in mass. It has been applied for the detection of viruses, bacteria, proteins, and nucleic acids due to their great sensitivity and selectivity (Borman 1987; Durmuş et al. 2015; Tilmaciu and Morris 2015).

4.4 Applications of Nanobiosensor

Nanobiosensor has diverse applications in various fields like biomedical, environmental, and agricultural industry, etc., as highlighted in Fig. 4.5. Blood glucose sensing is the most common and major application in biosensing due to its plentiful market potential. Biosensors have incredible market value in other fields, but commercial adoption was slow due to several technological difficulties. Biosensor contamination is a major problem, due to the presence of biomolecules along with semiconductor materials.

Fig. 4.5
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Diverse applications of nanobiosensor

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Current developments in the field of nanoelectronics, biological, and information technology present way to develop medical nanorobots which are implanted and incorporated devices. The nanorobotics consists of main sensing, actuation, data transmission, remote control uploading, and coupling power supply subsystems (Appenzeller et al. 2002; Cavalcanti et al. 2007; Freitas 1999; Lavan et al. 2003; Liu and Shimohara 2007; Shi et al. 2007). Nanorobots should offer new tools for common medical treatments because it has nanoscopic quality (Leary et al. 2006; Patel et al. 2006). Table 4.1 lists different nanomaterials used for fabricating nanobiosensor with various sensing techniques and applications in diverse fields.

Table 4.1 Table summarizes different nanomaterials used for fabricating nanobiosensor
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4.4.1 Detection of Glucose/Other Metals

Conventional methods are often tiresome in diabetes detection and monitoring. To eliminate this problem, the nanorobot sensor should be used to sense biological changes linked with hyperglycemia as it generates proteomic-based information (Cavalcanti et al. 2008). This will also make it possible to treat diabetes more quickly and effectively (Cash and Clark 2010; Gordijo et al. 2011; Samuel et al. 2010). Recently, Yang et al developed a very sensitive colorimetric detection method to detect early diabetes analysis by glucose detection in urine as an alternative of the blood sample, which can prevent the painful blood collection and infection risks. They projected a method to couple Fe/Pd/rGO with a portable paper sensor for urine glucose detection. From this method urine glucose was sensitively detected in a broad range of 1–200 μM with a limit of detection of 1.76 μM. The color difference with increasing concentration of urine glucose was easily visualized by naked eyes, which is significant to its realistic usage in screening and diagnosis of diabetes in early-stage (Yang et al. 2019).

Song et al. developed a novel strategy for clinical detection of Zn2+ in the human body based on the “on–off–on” ratiometric fluorescent nanosensor using the coupled quantum dots-carbon dots (Song et al. 2018). Copper is directly associated with liver damage; therefore, it is necessary to develop a simple and sensitive strategy to detect copper ions (Cu2+) in liver cells.

Lu et al. developed hydrophobic carbon dots (HCDs)-based dual-emission fluorescent probe for Cu2+ detection. The developed probe showed high sensitivity and selectivity to Cu2+ above former substances, and it was used to determine the changes of Cu2+ level in liver cells (Lu et al. 2017). Qian et al. developed a QDs nanosensor for the detection of 2,4,6-trinitrotoluene (TNT) explosives concentration over a range of 10 nM to 8 μM with a low detection limit of 3.3 nM. One can perform onsite visual determination of TNT with a high resolution because the ratiometric fluorescence nanosensing system exhibited visible fluorescence color changes (Qian et al. 2016).

4.4.2 Detection of Biomolecular Interaction

The elevated sensitivity of the localized surface plasmon resonance (LSPR) spectrum of nanomaterials to adsorbate induced changes in the local refractive index is being used to develop a different class of nanobiosensors or chemosensor (Baida et al. 2009; Brockman et al. 2000; Huang et al. 2009; Nguyen et al. 2015).The optical biosensor detects changes in local refractive index prototypical immunoassay involving biotin (B) and anti-biotin (AB) by monitoring the LSPR (Riboh et al. 2003). Liu et al. (2018b) studied an improved biomolecular interaction analysis probing with an incorporated array fluorescent biosensor with a wide range of low to high concentrations of anti-bisphenol A (BPA) antibody. This scheme is characterized by its high-throughput cross-reactivity analysis between antigens and antibodies on the patterned waveguide with a shortened time-to-result (Liu et al. 2018b). Recently, Zhang et al. prepared biosensor by Ag nanocubes/chitosan composite for the detection of mouse IgG and used to amplify the SPR signal (Zhang et al. 2016). A direct reasonable enzyme-linked immunosorbent assay format was developed and optimized on the surface of a carbon electrode by immobilizing the antibody using an electro-deposition of gold nanoparticles conjugated with polyclonal anti-tetracycline antibodies for detection of tungro disease in paddy plantations (Uda et al. 2019).

4.4.3 Pathogenic Bacteria Detection

Traditionally, bacteria identification in culture and biochemical testing are based on morphology. However, these methods are tiresome and occasionally all bacteria do not grow in culture and therefore the method of detection of bacteria in clinical samples needs to be developed. Magnetic nanoparticles have been used for the identification of Mycobacterium avium spp. paratuberculosis (MAP) through magnetic relaxation by Kaittanis et al. (2007). Nanobiosensor can be used for direct detection of the pathogenic agent while indirect detection is achievable by evaluating the pathogen’s metabolic activity by monitoring the nutrient utilization rate in solution. The dextran-coated gold nanoparticle-based technique is used for the measurement of antimicrobial susceptibility (Nath et al. 2008). Salmonella was detected by a gold/silicon nanorods immobilized with dye molecules (Fu et al. 2008). The dye molecules immobilized with silicon nanorods produced fluorescence when it comes in contact with Salmonella. This method has remarkable potential in biomedical diagnostics.

Some researcher has also developed a protocol for a simpler diagnostic technique for bacteria. These techniques have unique features that combine magnetic and fluorescent parameters in a nanoparticle-based platform. The magneto-fluorescent nanosensor (MFnS) has been developed that detected E. coli O157:H7 contamination with very high sensitivity, 1 colony-forming unit present in water can be detected (Banerjee et al. 2016; Shelby et al. 2017). This method has also been used to detect and quantify the pathogen contamination in both early- and late-stage contamination (Song et al. 2016).

4.4.4 Application in Cancer Biology

Early cancer detection and cure is a rising and attractive ground for research in plasmonic nanobiosensor. Telomerase is a specific reverse transcriptase enzyme containing catalytic subunit and RNA component that maintains the length and function of the telomer together with the proteins associated with the telomere (Greider and Blackburn 1985; Van Steensel and De Lange 1997; Van Steensel et al. 1998). Eventually, a critical telomere length is reached in normal cells, inducing cellular senescence and ultimately leading to apoptosis. In most malignancies, high levels of telomerase activity are found and are thought to play an important role in tumorigenesis (Bodnar et al. 1998; Counter et al. 1998; Kim et al. 1994; Shay and Bacchetti 1997). Telomere dysfunction also causes genetic instability with complex cellular and molecular responses involving checkpoints and apoptosis pathways for the retinoblastoma gene/p53 (Lan et al. 2003; Leri et al. 2003). Grimm et al have developed a magnetic-based nanobiosensor for fast screening of telomerase activity in biological samples (Gullberg et al. 2004). The telomerase-synthesized telomeric repeats (TTAGGG) annealed upon nanoparticles to change their magnetic state (a phenomenon readily detectable by magnetic readers), the developed magnetic nanosensor can determine telomerase activity. Recently, an optical fiber nanobiosensor was built to efficiently sense a broad-spectrum cancer biomarker, telomerase with its nanoscale tip at a single cell level (Zheng and Li 2010).

Injectable biosensors might be providing a new concept for prostate cancer biomarkers by querying the status of the prostate via a non-invasive readout. Proteases enzyme plays an important role in every characteristic of cancer; its activities could act as biomarkers. Dudani et al. developed a nanosensor library by a panel of prostate cancer proteases through transcriptomic and proteomic analysis that detect protease activity in vitro and in vivo using fluorescence and urinary readouts (Dudani et al. 2018). The impact of nanomaterials on the accuracy of biosensors in early detection of cancer such as lung, prostate, breast, and other cancers was discussed and reviewed by Sharifi et al. The modification of electrode performance by nanomaterials, however, is relatively complicated, resulting in limitations on the use of certain nanomaterials in biosensor applications (Sharifi et al. 2018).Wang et al. developed a small device that facilitated fast and straight analysis of the specific binding of small molecules to proteins using silicon nanowire (SiNW) field-effect transistor (FET) devices (Wang et al. 2005). Chandra et al. designed a sensor probe made-up by immobilizing monoclonal permeability glycoprotein antibody on the gold nanoparticles (AuNPs) conducting polymer composite to detect cancer cells between 50 and 100,000 cells/ml with the detection limit of 23 ± 2 cells/ml (Chandra et al. 2015). Thus, nanosensor can help in the diagnosis of fatal diseases like cancer at an early stage.

4.5 Conclusions and Future Prospects

There is a great demand of analytical devices for rapid, reliable, and economical detection of substances in biological fluids. These devices will be commercialized only if they can be used by a common man rather than by centralized labs or doctor’s clinics; biosensors are competent enough to solve these issues. Although biosensors have applications in various fields, their use in health care monitoring is the most important. Nanobiosensor is probed containing immobilized biological molecules on the nanomaterial. They can be used in the detection of microorganisms, pollutants, molecular biomarkers, and monitoring of metabolites in body fluids. Different kinds of nanomaterials like metal, QD, graphene, carbon nanotubes, etc., can be used in the biosensor, each having its own characteristic property. For example, the SPR property of metal nanoparticles is exploited in optical biosensors. Most of the biosensors which are commercialized are enzyme-based sensor as enzymes are highly specific biomolecules. Developments of fabrication methods for nanomaterials which are nontoxic and economically viable are required. Research is required to improve the properties of the nanobiosensor so that it can detect and quantify biological fluids without multiple calibrations using clinical samples. Efforts should be made to improve the sensitivity of detection with high sensitivity. Thus, nanobiosensor should be low cost, disposable, reliable, and easy to use that can be utilized for in-home medical diagnosis of diseases.