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Rapid detection of antibodies to SARS-CoV-2 is critical for COVID-19 diagnostics, epidemiological research, and studies related to vaccine evaluation. It is known that the nucleocapsid (N) is the most abundant protein of SARS-CoV-2 and can serve as an excellent biomarker due to its strong immunogenicity. This paper reports a rapid and ultrasensitive 3D biosensor for quantification of COVID-19 antibodies in seconds via electrochemical transduction. This sensor consists of an array of three-dimensional micro-length-scale electrode architecture that is fabricated by aerosol jet 3D printing, which is an additive manufacturing technique. The micropillar array is coated with N proteins via an intermediate layer of nano-graphene and is integrated into a microfluidic channel to complete an electrochemical cell that uses antibody-antigen interaction to detect the antibodies to the N protein. Due to the structural innovation in the electrode geometry, the sensing is achieved in seconds, and the sensor shows an excellent limit of detection of 13 fm and an optimal detection range of 100 fm to 1 nm. Furthermore, the sensor can be regenerated at least 10 times, which reduces the cost per test. This work provides a powerful platform for rapid screening of antibodies to SARS-CoV-2 after infection or vaccination.

Rapid detection of antibodies during infection and after vaccination is critical for the control of infectious outbreaks, understanding immune response, and evaluating vaccine efficacy. In this manuscript, we evaluate a simple ultrarapid test for SARS-CoV-2 antibodies in COVID-19 patients, which gives quantitative results (i.e., antibody concentration) in 10-12 s using a previously reported nanomaterial-based three-dimensional (3D)-printed biosensing platform. This platform consists of a micropillar array electrode fabricated via 3D printing of aerosolized gold nanoparticles and coated with nanoflakes of graphene and specific SARS-CoV-2 antigens, including spike S1, S1 receptor-binding domain (RBD) and nucleocapsid (N). The sensor works on the principle of electrochemical transduction, where the change of sensor impedance is realized by the interactions between the viral proteins attached to the sensor electrode surface and the antibodies. The three sensors were used to test samples from 17 COVID-19 patients and 3 patients without COVID-19. Unlike other serological tests, the 3D sensors quantitatively detected antibodies at a concentration as low as picomole within 10-12 s in human plasma samples. We found that the studied COVID-19 patients had higher concentrations of antibodies to spike proteins (RBD and S1) than to the N protein. These results demonstrate the enormous potential of the rapid antibody test platform for understanding patients' immunity, disease epidemiology and vaccine efficacy, and facilitating the control and prevention of infectious epidemics.

Microfluidics is revolutionizing the way research on cellular biology has been traditionally conducted. The ability to control the cell physicochemical environment by adjusting flow conditions, while performing cellular analysis at single-cell resolution and high-throughput, has made microfluidics the ideal choice to replace traditional

A dual-modality microfluidic biosensor is fabricated using a mesoporous nanostructured cysteine–graphene hydrogel for the quantification of human cardiac myoglobin (cMb). In this device, the nanoengineered mesoporous L-cysteine–graphene (Cys–RGO) hydrogel performs the role of a dual-modality sensing electrode for the measurements conducted using differential pulse voltammetry and surface plasmon resonance (SPR) techniques. High surface reactivity, mesoporous structure and fast electron transfer combined with good reaction kinetics of the graphene hydrogel in this device indicate excellent performance for the detection of human cardiac myoglobin in serum samples. In electrochemical modality, this microfluidic chip exhibits a high sensitivity of 196.66 μA ng−1 mL cm−2 for a linear range of concentrations (0.004–1000 ng mL−1) with a low limit of detection (LOD) of 4 pg mL−1 while the SPR technique shows a LOD of 10 pg mL−1 for cMb monitoring in the range 0.01–1000 ng mL−1. The intra-assay coefficient of variation was less than 8% for standard samples and 9% for real serum samples, respectively. This Cys–RGO hydrogel-based microfluidic SPR chip allows real-time dynamic tracking of cMb molecules with a high association constant of 4.93 ± 0.2 × 105 M−1 s−1 and a dissociation constant of 1.37 ± 0.08 × 10−4 s−1, self-verification, reduced false readout, and improved detection reliability.

There is an unmet need for improved fertilizer management in agriculture. Continuous monitoring of soil nitrate would address this need. This paper reports an all-solid-state miniature potentiometric soil sensor that works in direct contact with soils to monitor nitrate-nitrogen (NO3--N) in soil solution with parts-per-million (ppm) resolution. A working electrode is formed from a novel nanocomposite of poly(3-octyl-thiophene) and molybdenum disulfide (POT-MoS2) coated on a patterned Au electrode and covered with a nitrate-selective membrane using a robotic dispenser. The POT-MoS2 layer acts as an ion-to-electron transducing layer with high hydrophobicity and redox properties. The modification of the POT chain with MoS2 increases both conductivity and anion exchange, while minimizing the formation of a thin water layer at the interface between the Au electrode and the ion-selective membrane, which is notorious for solid-state potentiometric ion sensors. Therefore, the use of POT-MoS2 results in an improved sensitivity and selectivity of the working electrode. The reference electrode comprises a screen-printed silver/silver chloride (Ag/AgCl) electrode covered by a protonated Nafion layer to prevent chloride (Cl-) leaching in long-term measurements. This sensor was calibrated using both standard and extracted soil solutions, exhibiting a dynamic range that includes all concentrations relevant for agricultural applications (1-1500 ppm NO3--N). With the POT-MoS2 nanocomposite, the sensor offers a sensitivity of 64 mV/decade for nitrate detection, compared to 48 mV/decade for POT and 38 mV/decade for MoS2. The sensor was embedded into soil slurries where it accurately monitored nitrate for a duration of 27 days.

Cardiovascular diseases (CVDs) are the leading causes of death worldwide. Cardiac troponin I (cTnI) is a cardiac biomarker exploited extensively for early diagnosis of acute myocardial infarction (AMI). We report a highly sensitive microfluidic biosensor for the electrochemical detection of human cTnI in real patient samples. In this device, a patterned mesoporous nickel vanadate hollow-nanosphere modified chitosan (Ch-Ni3V2O8) was integrated with a microfluidic structure. Owing to its excellent redox activity and biocompatibility, larger surface, and tunable oxidation states (V5+, V4+, and V3+), the Ch-Ni3V2O8 matrix was used to functionalize the cardiac antibodies of troponin I (cAb) and amplify the electrochemical readouts. This device offered a high sensitivity of 38.88 μA ng−1 mL−1 cm−2 at a wide range of cTnI concentrations (0.005–100 ng mL−1). A low limit-of-detection of 5 pg mL−1 and high stability, high reproducibility and good selectivity were achieved due to integration of microfluidic elements with a hollow-nanosphere Ch-Ni3V2O8. This microfluidic device can be implemented to detect B-type natriuretic peptide, myoglobin, cardiac troponin C, and cardiac troponin T by functionalizing the specific antibody recognition elements and could be used for real point-of-care applications in biomedicine.

We report here leukemia biomarker detection by monitoring the charge transfer dependent Fermi level fluctuation due to adsorption of chemical or biological species at semiconductor surface, leading to detection of CML at an early stage. This technique demonstrates a new way to understand the operation of biosensor, where an in-depth analysis is presented here to understand the sensing mechanism. The sensor performance is optimized by tuning silane binding time, antibody concentration and its binding time on the CNTs surface. In every step during adsorption of chemical and biological molecules, complementary studies such as Raman, FTIR and FESEM analysis were done to cross check the claim. This sensor shows a lower limit-of-detection (LOD) of 27 cells/ml within a concentration range of CML cells (1.1 × 107–2 × 103cells/mL). The obtained data are equally competitive to the reported sensors relying on other conventional techniques where a series of rigorous steps were followed to obtain the expected data. Thus, the use of photoconductivity measurement to monitor the Fermi level fluctuation in CNTs for detection of target species proves to be a unique sensitive platform, less prone to contamination and human error unlike the conventional techniques and can be used for point-of-care cancer diagnostics.

Two dimensional nanomaterials such as molybdenum disulfide (MoS2) has gained significant interest in designing electrochemical devices for biosensing application. In this work, we have designed cetyltrimethyl ammonium bromide (CTAB) functionalized MoS2 nanosheets (CTAB-MoS2-NS) for conjugation of protein on the microfluidics electrode for Salmonella typhimurium (S.typhimurium) detection. MoS2 nanosheets from the bulk MoS2 were synthesized using CTAB assisted exfoliation methods resulting into positive charge on the CTAB-MoS2-NS. Further, optical and electron microscopic studies of CTAB-MoS2-NS reveal, its suitability for biosensing application. These CTAB-MoS2-NS were deposited onto the patterned hydrolyzed indium tin oxide (ITO) microelelctrode, utilizing the strong electrostatic interaction with the positively charged CTAB-MoS2-NS. Then microelectrode has been integrated with polydimethylsiloxane (PDMS) microfluidic device to design a Lab on a Chip platform for S.typhimurium detection. Detection of the S.typhimurium cells have been performed using electrochemical impedance spectroscopy (EIS) technique. The fabricated microfluidic immunosensor offers highly improved biosensing parameters, as sensitivity was found to be 1.79 kΩ/CFU−1 mL cm−2 with the detection limit 1.56 CFU mL−1in the wide detection range of 101–107 CFUmL−1.

A sensitive and selective microfluidic immunochip was fabricated for detection of Salmonella typhimurium ( S. typhimurium ) bacterial cells. In this sensor, graphene oxide (GO) nano sheets wrapped carboxylated multiwalled carbon nanotubes (cMWCNTs) composite acted as a transducer material. The colloidal solution of GO-cMWCNTs composite was selectively deposited onto patterned indium tin oxide (ITO) electrode and sealed with polydimethylsiloxane (PDMS) micro channels. The S. typhimurium antibodies (StAb) were in situ biofunctionalized followed by EDC-NHS covalent chemistry via amidation reaction. The presence of abundant functional groups at the GO-cMWCNTs composite improved the loading of antibodies (StAb) against S . typhimurium leading to improved biosensing characteristics. Wrapping of cMWCNTs with GO resulted in superior electron transfer behavior enhancing the sensitivity (162.47 μA/CFU −1 /mLcm −2 ) almost two folds as compared to that based on GO (89.16 μA/CFU −1 /mLcm −2 ) sheets for bacterial cells detection. Besides this, GO wrapped cMWCNTs integrated microfluidics biosensor offered low detection limit as 0.376 CFU/mL and negligible interference due to presence of Escherichia coli ( E. coli (O157:H7).

Additive manufacturing, also called 3D printing, is a rapidly evolving technique that allows for the fabrication of functional materials with complex architectures, controlled microstructures, and material combinations. This capability has influenced the field of biomedical sensing devices by enabling the trends of device miniaturization, customization, and elasticity (i.e., having mechanical properties that match with the biological tissue). In this paper, the current state‐of‐the‐art knowledge of biomedical sensors with the unique and unusual properties enabled by 3D printing is reviewed. The review encompasses clinically important areas involving the quantification of biomarkers (neurotransmitters, metabolites, and proteins), soft and implantable sensors, microfluidic biosensors, and wearable haptic sensors. In addition, the rapid sensing of pathogens and pathogen biomarkers enabled by 3D printing, an area of significant interest considering the recent worldwide pandemic caused by the novel coronavirus, is also discussed. It is also described how 3D printing enables critical sensor advantages including lower limit‐of‐detection, sensitivity, greater sensing range, and the ability for point‐of‐care diagnostics. Further, manufacturing itself benefits from 3D printing via rapid prototyping, improved resolution, and lower cost. This review provides researchers in academia and industry a comprehensive summary of the novel possibilities opened by the progress in 3D printing technology for a variety of biomedical applications. [ FROM AUTHOR] Copyright of Advanced Functional Materials is the property of John Wiley & Sons, Inc. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full . (Copyright applies to all Abstracts.)

This paper reports an integrated dual-modality microfluidic sensor chip, consisting of a patterned periodic array of nanoposts coated with gold (Au) and graphene oxide (GO), to detect target biomarker molecules in a limited sample volume. The device generates both electrochemical and surface plasmon resonance (SPR) signals from a single sensing area of Au-GO nanoposts. The Au-GO nanoposts are functionalized with specific receptor molecules, serving as a spatially well-defined nanostructured working electrode for electrochemical sensing, as well as a nanostructured plasmonic crystal for SPR-based sensing via the excitation of surface plasmon polaritons. High sensitivity of the electrochemical measurement originates from the presence of the nanoposts on the surface of the working electrode where radial diffusion of redox species occurs. Complementarily, the SPR detection allows convenient tracking of dynamic antigen-antibody interactions, to describe the association and dissociation phases occurring at the sensor surface. The soft-lithographically formed nanoposts provide high reproducibility of the sensor response to epidermal growth factor receptor (ErbB2) molecules even at a femtomolar level. Sensitivities of the electrochemical measurements to ErbB2 are found to be 20.47 μA μM

Electrospinning was employed to synthesize a Ag nanoparticle (NP)-impregnated partially aligned and free-standing carbon nanofibers (CNFs) mat using a polyacrylonitrile (PAN) and silver nitrate blend followed by carbonization. Pyrolyzation of the PAN/AgNO 3 blend produced the nanoporous CNFs, and the Ag NPs were grown within the CNFs via thermal decomposition of AgNO 3 . The fiber diameters of the synthesized CNFs ranged from 130 to 190 nm, and the size of the impregnated Ag NPs was ∼30 nm. The presence of the Ag NPs enhanced the electrical conductivity and promoted graphitization of the CNFs via the templating effect of the Ag NPs. These synthesized CNFs and AgCNFs nanocomposite were electrophoretically deposited onto indium tin oxide electrodes for detection of triglyceride molecules. Oxygen plasma treatment of the CNFs and AgCNFs surfaces resulted in enhanced loading of lipase and glycerol dehydrogenase bienzymes. The AgCNFs nanocomposite exhibited faster electron transfer than the CNFs, as corroborated by electrochemical impedance spectroscopy and cyclic voltammetry studies. Covalent functionalization via 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide/ N -hydroxysuccinimide coupling chemistry on a nanoporous CNFs surface led to higher stability of the fabricated biosensor toward triglyceride detection. The sensitivity was four-fold higher for the AgCNFs (1.232 μA mg/dL −1 cm −2 ) bioelectrode compared with the CNFs (0.33 μA mg/dL −1 cm −2 ) over a wide detection range (25–500 mg/dL). These biosensors exhibited excellent selectivity, good reproducibility, and faster response (10 s). Thus, enhanced graphitization and electrical conductivity of nanoporous CNFs via incorporation of Ag NPs yields a promising platform for the detection of triglyceride (TG) biomolecules.

The authors describe a nanostructured hybrid platform for amperometic determination of the plasticizer bisphenol A (BPA). It consists of two dimensional sheets of reduced graphene oxide (rGO) that are decorated with Mn3O4 nanoparticles. The enzyme tyrosinase was immobilized on the surface of the hybrid nanosheets placed on an ITO electrode. The larger surface area and enhanced charge transfer properties of the rGO/Mn3O4 nanosheets provide a synergistic effect that results in excellent sensing performance including fast electron transfer kinetics, high electroactivity, good reproducibility and selectivity compared to other electrodes of that kind. Figures of merit include a sensitivity of 93.2 μA⋅nM−1⋅cm−2, an analytical range that extends from 0.01 to 100 μM, and a 10 nM lower detection limit. Its long-term stability of 8 weeks suggests the use of such enzyme electrodes as potential tools in clinical diagnostics.

Nitrate is a major macronutrient for plant growth. There is a high demand to develop robust, reliable, and maintenance-free soil sensors for long-term monitoring of nitrate variations in field. An ion-selective membrane-based solid-state nitrate sensor is developed using poly(3-octyl-thiophene)-molybdenum disulfide nanocomposite as an ion-to-electron transducing layer. The sensor offers a high sensitivity of 64 mV/decade, a dynamic range of 1–1500 ppm NO 3 --N, and an improved selectivity for nitrate detection in soils. The sensor has demonstrated the ability to continuously monitor soil nitrate concentrations over a period of four weeks.

This paper reports a low-cost extended-gate field effect transistor based nitrate sensor using a microfluidic channel based Reference Electrode (µcRE). The µcRE is integrated with a MOSFET to increase potential stability for long-term measurement. The sensor also includes a readout circuit to save or remotely transmit data to a smartphone. The µcRE exhibits a 0.5 mV/hour drift rate and the sensor offers a 0.997 R-Squared value to the linear fitting for potentiometric measurement of nitrate in water.

4-Nitrophenol(4-NP) is a highly toxic and hazardous substance which has a negative impact on human organs including kidney, lung, liver, blood and nervous system. Thus, its low concentration quantification with better accuracy and low testing cost is high desirable. We report on the fabrication of an electrochemical sensor for detection of 4-NP without incorporating any enzyme. The sensor comprises of highly crystalline silver doped cerium oxide (CeO2:Ag) nanoparticles (NPs; size∼ 8−10 nm) which have been synthesized by a low-cost co-precipitation method. A glassy carbon electrode (GCE) was used in this study as a 4-NP sensitive electrode wherein the electrode was modified with CeO2 with and without Ag NPs. The enhanced electro-oxidation properties due to existence of mixed Ce3+ and Ce4+ valence states, high surface area, high crystallinity, and direct electron transfer properties of CeO2:Ag NPs improved the sensing efficacy for nitrophenol (NP)detection. The sensor provided high sensitivities (4.8 μA/uM and 1.2 μA/μM) and a low limit of detection for detection of 4-NP with a wide range of concentration (7.8 μM–1000 μM). The synthesized CeO2:Ag NPs based electrode could be potentially used for sensitive detection of other hazardous substances.

We report a universal protocol for the in situ bioinspired green synthesis of metal (Pd, Pt, Ag and Au) nanoparticles (mNPs) on simultaneously reduced graphene oxide (rGO) sheets using a black pepper extract (BPE) for quantification and kinetic analysis of epidermal growth factor receptor (ErbB2) for application to breast cancer diagnostics. The phytochemicals present in BPE were found to assist the reduction, stabilization, and surface addition of mNPs onto rGO sheets. The antioxidants present in the BPE assist the formation of a "green corona" on the surface of derived G-mNPs@rGO (G-Pd@rGO, G-Pt@rGO, G-Ag@rGO, and G-Au@rGO) sheets as corroborated by DLS and FT-IR experiments. These bioinspired derivatives provided biocompatible surfaces, resulting in higher cell viability compared to that of chemically derived composites, C-mNPs@rGO (C-Pd@rGO, C-Pt@rGO, C-Ag@rGO, and C-Au@rGO). Toxicity was found to be drastically reduced for green-corona assisted derivatives of GO due to strong antioxidant properties of the phytochemicals present in BPE. In addition, a comparative analytical study of the quantification and kinetics of breast cancer biomarkers using both G-mNPs@rGO and C-mNPs@rGO nanocomposites was carried out. The G-mNPs@rGO nanosheets can be employed for ultrasensitive detection of ErbB2 concentration from 1.0 fM to 0.5 μM.

We report results of the studies relating to fabrication of an electrochemical biosensor platform based on in-situ electrosynthesized manganese oxide (Mn3O4)-polyaniline (PANI) nanofibers for detection of bisphenol A (BPA), an endocrine disrupting chemical. The spherical Mn3O4 nanoparticles synthesized using cetyltrimethylammoniumbromide were modified with PANI in presence of polyvinyl sulphonic acid and glutaraldehyde. The tyrosinase (Tyrs) molecules covalently immobilized on the PANI-modified Mn3O4 nanofibers surface were characterized using X-ray diffraction, electron microscopy and Fourier transform infrared spectroscopy. This electrochemical biosensor exhibits a response time of 20 s, sensitivity of 0.776 mA μM−1 L cm−2, respectively, and 0.134 mA μM−1 L cm−2 in the concentration ranges, 0.004–0.09 × 10−6 mol L−1 and 0.2–0.8 × 10−6 mol L−1 of BPA.

We present a straightforward method for fabricating functional micro-, submicro-, and nano-channels embedded in a porous carbon film and the application of this microfluidic platform for electrochemical sensing. A skin layer of poly(methyl methacrylate) (PMMA) fibers was first electrospun on a thoroughly cleaned Si wafer substrate, followed by spin coating of a polyacrylonitrile (PAN) film on top of the skin. High-temperature carbonization of the composite film decomposed the PMMA fibers and produced embedded microchannels in the PAN-derived amorphous monolithic carbon electrode. The channels were decorated with Pt nanoparticles by in situ thermal decomposition of a precursor metal salt to enhance functionality of the carbon electrode. Carbon electrodes decorated with Pt nanoparticles (carbon-Pt), with and without embedded microchannels, were used to detect the food toxin aflatoxin B1 (AFB1) by surface biofunctionalization with the antibodies of AFB1 (anti-AFB1) via an electrochemical impedance technique. The aligned nanochannels in the porous carbon film act as a reaction chamber for antigen–antibody interactions and provide channels for fast electron transport toward the electrode from the electrolyte, resulting in improved electrochemical performance of the biosensor. The fabricated immunosensor is highly sensitive to 1 pg/mL of AFB1 with a concentration range of 10−12–10−7 g/mL.

A label-free, highly reproducible, sensitive, and selective biosensor is proposed using antiapolipoprotein B 100 (AAB) functionalized mesoporous few-layer reduced graphene oxide and nickel oxide (rGO-NiO) nanocomposite for detection of low density lipoprotein (LDL) molecules. The formation of mesoporous rGO-NiO composite on indium tin oxide conductive electrode has been accomplished via electrophoretic technique using colloidal suspension of rGO sheets and NiO nanoparticles. This biosensor shows good stability obtained by surface conjugation of antibody AAB molecules with rGO-NiO matrix by EDC-NHS coupling chemistry. The defect-less few layer rGO sheets, NiO nanoparticles (nNiO) and formation of nanocomposite has been confirmed by Raman mapping, electron microscopic studies, X-ray diffraction, and electrochemical techniques. The synthesized rGO-NiO composite is mesoporous dominated with a small percentage of micro and macroporous structure as is evident by the results of Brunauer-Emmett-Teller experiment. Further, the bioconjugation of AAB with rGO-NiO has been investigated by Fourier transform-infrared spectroscopy studies. The kinetic studies for binding of antigen-antibody (LDL-AAB) and analytical performance of this biosensor have been evaluated by the impedance spectroscopic method. This biosensor exhibits an excellent sensitivity of 510 Ω (mg/dL)(-1) cm(-2) for detection of LDL molecules and is sensitive to 5 mg/dL concentration of LDL in a wide range of 0-130 mg/dL. Thus, this fabricated biosensor is an efficient and highly sensitive platform for the analysis of other antigen-antibody interactions and biomolecules detection.

A novel, green, and sustainable route has been introduced for biosynthesis of a palladium nanoparticles (PdNPs) anchored reduced graphene oxide (rGO) platform for protein conjugation and detection of triglycerides. Fenugreek seeds (FS) were utilized for the simultaneous green reduction of Pd salt and graphene oxide (GO), which also act as a stabilizing and decorating agent for in situ grown PdNPs on rGO sheets. The well dispersed, homogeneous, and biologically reduced PdNPs having an average size of 3.5 nm on the rGO sheets are electrophoretically deposited on an indium tin oxide (ITO) glass substrate. The biosynthesized Pd-rGO sheets were characterized using spectroscopic and electrochemical techniques and further utilized for co-immobilization of lipase and glycerol dehydrogenase (LIP-GLDH) enzymes using EDC-NHS coupling chemistry. The LIP-GLDH conjugated Pd-rGO platform was used for electrochemical detection of triglycerides. The green and nontoxic approach offers enhanced stability of the fabricated b...

The paper reports on controlled formation of microscale wrinkles and ridges on the surface of a bioelectrode via mechanical stretching to tune and optimize the electrochemical sensing performances of graphene oxide (GO) based nitrate ion sensors. The bioelectrode consists of GO nanosheets drop-coated on a gold (Au) layer with a pre-stretched elastomer substrate. Enzyme nitrate reductase is used for covalent immobilization on the wrinkled-ridged GO surface. Upon relaxation from the pre-stretch, wrinkles or ridges are formed in the GO layer. As the pre-stretch increases, the sinusoidal wrinkles transform to localized ridges on the surface of bioelectrodes. Such morphological transitions, realized by simple mechanical stretching and relaxing, allow optimizing of the electrochemical current and sensing characteristics of the nitrate sensor. The sensing performances of the bioelectrodes at different pre-stretches are investigated. In addition to an increased electroactive surface area, the predominant localized ridges with small sinusoidal wrinkles formed on the GO surface provide a favorable spatial feature, enabling efficient radial diffusion of nitrate ions from surrounding analyte solutions onto the surface of the textured bioelectrode. At the pre-stretch of 8%, the nitrate sensor using the wrinkled-ridged bioelectrode exhibits a considerably high sensitivity of 0.224 μA L mol−1 cm−2 in response to nitrate ions, which is five times higher than that provided by the planar counterpart. Also, the textured bioelectrode shows high selectivity even in the presence of other inferring ions. The present nitrate sensor has potential applications in nitrate detection in sustainable agriculture, environmental monitoring, food analysis, and pharmaceutical industries.

We demonstrate the fabrication of a label-free immunosensor for electrochemical detection of mycotoxin i.e. aflatoxin B1 (AFB1) using nickel nanoparticle decorated reduced graphene oxide (rGO–Ni NPs) sheets. The rGO–Ni NPs have been electrophoretically deposited onto an indium tin oxide (ITO) coated glass electrode. This fabricated immunosensor is sensitive to 0.16 ng mL−1 concentration of AFB1 in phosphate buffer solution. It exhibits a lower limit of detection when compared to the HPLC standard method (2.5 ng mL−1) and shows minimal interference with another food toxin (ochratoxin A). Electron microscopy, Fourier transform infrared, UV-visible spectroscopy and electrochemical techniques were utilized to confirm selective decoration of Ni NPs on the rGO sheets and to investigate the chemical and electrochemical properties of the nanocomposite. The highly crystalline properties of the rGO–Ni NPs sheets along with the excellent electro-catalytic properties of the Ni NPs result in a higher heterogeneous electron transfer rate indicating the enhanced sensitivity (129.6 μA ng−1 mL cm−2) of the device. The favorable environment for antibody conjugation on the surface of the rGO–Ni NPs sheets offers a low limit-of-detection (0.16 ng mL−1) for AFB1.

We have fabricated a nanocomposite of reduced graphene oxide (rGO) sheets and chitosan (Cn) polymer based highly sensitive electrochemical biosensor for detection of bisphenol A (BPA). The two-dimensional structure and chemical functionality of rGO and Cn provide an excellent electrode surface for loading of tyrosinase enzyme molecules. This rGO–Cn nanocomposite is capable of effectively utilizing their superior conductivity, larger effective surface area and superior electrochemical performance due to its synergistic effect between rGO and Cn. The structural, morphological and electrochemical characterizations of nanocomposite sheets have been performed by electron microscopy, X-ray diffraction, FTIR and Potentiostat/Galvanostat techniques. This fabricated biosensor is sensitive to nanomolar (0.74 nM) concentration of BPA and detection time is 10 s compared to conventional BPA ELISA kit (0.3 µg/L and 2.5 h). The rGO–Cn based biosensor exhibits a higher sensitivity (83.3 µA nM−1 cm−2), wider linearity (0.01–50 µM) with good selectivity towards BPA. This biosensor is capable to quantify real sample of BPA using packaged drinking water bottles. This rGO–Cn nanocomposite sheets emerges as a potential electrode material for detection of other estrogenic substrate.

A label-free impedimetric lab on a chip (iLOC) is fabricated using protein (bovine serum albumin) and antiapolipoprotein B functionalized carbon nanotubes-nickel oxide (CNT-NiO) nanocomposite for low-density lipoprotein (LDL) detection. The antiapolipoprotein B (AAB) functionalized CNT-NiO microfluidic electrode is assembled with polydimethylsiloxane rectangular microchannels (cross section: 100 × 100 μm). Cytotoxicity of the synthesized CNTs, NiO nanoparticles, and CNT-NiO nanocomposite has been investigated in the presence of lung epithelial cancer A549 cell line using MTT assay. The CNT-NiO nanocomposite shows higher cell viability at a concentration of 6.5 μg/mL compared to those using individual CNTs. The cell viability and proliferation studies reveal that the toxicity increases with increasing CNTs concentration. The X-ray photoelectron spectroscopy studies have been used to quantify the functional groups present on the CNT-NiO electrode surface before and after proteins functionalization. The binding kinetic and electrochemical activities of CNT-NiO based iLOC have been conducted using chronocoulometry and impedance spectroscopic techniques. This iLOC shows excellent sensitivity of 5.37 kΩ (mg/dL)-1 and a low detection limit of 0.63 mg/dL in a wide concentration range (5-120 mg/dL) of LDL. The binding kinetics of antigen-antibody interaction of LDL molecules reveal a high association rate constant (8.13 M-1 s-1). Thus, this smart nanocomposite (CNT-NiO) based iLOC has improved stability and reproducibility and has implications toward in vivo diagnostics. (Chemical Presented).

Recent developments in plasmonic nanostructures have great importance in improving the sensing characteristics of optical sensors. Plasmonic nanostructures are widely used to develop optical nanobiosensors for quantitative detection of bio-species and their analysis. This may include medical diagnostics, food quality, and environmental monitoring. In this chapter, we demonstrate the basics of plasmonic nanostructured materials and their application in biosensors on the basis of surface plasmon response and localized plasmon response principles. Also we describe the integration of plasmonic nanostructures with fiber-optic technology for biosensing applications.

We have focused on the fundamentals and applications of biosensors in the preceding Chapters 1–9 Chapter 1 Chapter 2 Chapter 3 Chapter 4 Chapter 5 Chapter 6 Chapter 7 Chapter 8 Chapter 9 . The key challenges pertaining to the fabrication of point-of-care biosensors are that they should be easy to use, be handheld, be fast in analysis, be affordable, and have enhanced availability. The market for biosensors except for glucose sensors is slightly incremental with a low success rate. In this chapter, we discuss the potential issues in biosensors for commercialization with future prospects for development and end up with conclusions.

With remarkable advantages of nanostructured materials, there is a tremendous growth in development of DNA biochip–based devices for point-of-care applications. DNA chips have attracted significant interest as they enable miniaturization, fast analysis, and integration with biochemical assays. Coupled with high sensitivity, selectivity, and low sample volume, the integration of nanostructures into DNA biochips offer several features such as low-cost diagnostic tests, quick analysis, and simplicity and reduced assay times. In this chapter, we focus on the application of the nanostructured materials toward development of DNA biochips, microarrays, and RNA biosensors. Biochips are known as DNA chips, protein chips, and microfluidic chips. We will discuss basics and fundamentals of DNA biochips, various nucleic acid biosensors including DNA, peptide nucleic acid, RNA, and aptamers. We also cover the surface functionalization of nanomaterials with DNA molecules and the importance of nanomaterials for biosensing using different techniques.

With the recent advancement of nanomaterials and nanostructured materials, the point-of-care biosensor devices have shown a potential growth to revolutionize the future personalized health care diagnostics and therapy practices. This chapter deals with the fundamentals of nanomaterials-based biosensors. The first chapter covers the brief details of nanotechnology with its types and an introduction to the synthesis of nanomaterials and their importance to construct transducers. The different components of transducers such as electrochemical, optical, piezoelectric, thermal, surface plasmon resonance, and so on for biosensors have been explained in this chapter. Various principles utilized for development of enzymatic biosensors, immunosensors, DNA, and whole-cell biosensors have been included in this chapter. Immobilization of bioreceptors is a crucial step to fabricate biosensors and their stepwise demonstration and conjugation of nanomaterials with nanomaterials have been described.

Advanced functional nanocomposite materials have been found to play a major role in the development of biomolecular devices. Chemists, biologists, physicists, and materials scientists have been showing great interest to exploit the hybrid properties of smart nanocomposite materials by assembling their inorganic, organic, and biological properties into miniaturized biomolecular devices for health care diagnostics. Besides this, hybrid nanocomposites have been predicted to have promising applications in different fields including electronics, mechanics, protective coatings, catalysis, medicine, biotechnology, etc. Efforts are continuing to make new functional hybrid materials by researchers with exciting properties in biosensor fields. In this chapter, we discuss different aspects of hybrid nanocomposites, their formation, and applications for biomolecular devices.

Polymers have been considered as insulating materials for the past 40 years. With a simple modification, polymers can conduct electricity like metals. Nanostructures of conducing polymers prepared by several methods including hard-template, soft-template, and other methods can be conjugated with bio-species for construction of biosensing devices. Biopolymeric nanostructured materials have recently received much attention in nanoscience and nanotechnology due to their unique and tunable electrochemical and optical properties. Among the various nanobiomaterials, nanostructured conducting polymers (nCPs) are getting increasing interest for the development of biosensors due to biocompatibility in cellular environments. Many nCPs have been projected to have applications in clinical diagnostics. This chapter describes the salient features of nCPs for applications in biosensors and bioimaging.

Biomaterials are natural materials that can be utilized to replace and aid the functions of a body part or a entire organ system and that which remains in contact with the living cells or tissues without inducing a toxic response. The nanostructured biomaterials are being intensely investigated for the development of both in vivo and in vitro biosensors. This chapter focuses on the biosynthesis of the various nanostructures and their applications toward development of in vivo biosensors. Several issues associated with the development of in vivo biosensors are explained in this chapter. Besides this, efforts have been made to discuss the characteristics of different nanostructured biomaterials including metallic, polymeric, composite, carbon, and ceramic for application in in vivo biosensing and bioimaging.

In recent years, nanostructured metal/metal oxides–based immunosensors have gained unprecedented growth with fast detection, high sensitivity, and portability for detection of biomolecules (enzymes, antibodies, proteins, etc.). In particular, nanostructured metal oxides–based electrochemical immunosensors offer several advantages such as enhanced loading of desired biomolecules due to their larger surface area, biocompatibility, low cost, and fast analysis. The utilization of nanostructured metals in electrochemical- and optical-based immunosensors has been exploited due to the multifunctional properties of nanostructured metals. Nanostructured metals provide multilabel amplification, high densities of captured bio-species, multiplexing capability for simultaneous measurements of multiple biomarkers via microarrays, and detection of minute concentration of desired biomolecules. In this chapter we describe details of the nanostructured metals/metal oxides for development of immunosensors.

A sensitive, reproducible, stable and label-free immunosensor has been prepared via simultaneous reduction of graphene oxide and gold(III) salt using an eco-friendly and non-toxic reducing agent sodium citrate resulting in uniformly distributed gold nanoparticles on reduced graphene oxide (rGO) sheets. The in situ grown gold@carboxylated reduced graphene oxide (Au@rGO) surface has been used for bioconjugation with monoclonal antibodies of aflatoxin B1 using EDC-NHS chemistry. The in situ growth of AuNPs (gold nanoparticles) onto the rGO sheet results in improved electrocatalytic activity and loading of the antibodies due to the enhanced surface area. The monodispersion of the Au nanoparticles on the rGO sheets yields heterogeneous electron transfer (2.85 × 10−4 cm s−1) resulting in improved biosensor efficacy compared to that based on the rGO electrode. This immunosensor is sensitive to detect as low as 0.1 ng mL−1 concentration of aflatoxin compared to the reported ELISA (enzyme-linked immunosorbent assay) standard method. The Au@rGO based immunosensor exhibits high sensitivity (182.4 μA (ng mL−1)−1 cm−2) in a wide linear detection range of 0.1–12 ng mL−1. Results of the studies related to this immunosensor reveal that the Au@rGO nanocomposite is a suitable platform for the development of a compact biosensing device for food toxin monitoring.

We present a highly sensitive and selective electrochemical sandwich immunosensor (the analyte is “sandwiched” between two antibodies) based on chitosan (CH) modified nickel oxide (NiO) nanoparticles for the detection of Vibrio cholerae (Vc). The primary monoclonal antibodies specific to Vibrio cholerae (Ab-Vc) and bovine serum albumin (BSA) were co-immobilized on a CH–NiO surface deposited onto an indium tin oxide (ITO) coated glass electrode. The specific binding of Ab-Vc towards Vc was confirmed by interaction of secondary antibodies conjugated with protein [horse radish peroxidase (HRP)], with varying concentrations of hydrogen peroxide (H2O2), via electrochemical as well as optical techniques. The CH–NiO/ITO and Ab-Vc/CH–NiO/ITO electrodes have been characterized using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy and electrochemical techniques. This immunoelectrode (BSA/Ab-Vc/CH–NiO/ITO) exhibits a detection range of 20–700 ng mL−1 with a sensitivity of 0.644 μA ng mL−1 cm−2 and a low detection range of 0.108 ng mL−1 to Vc concentration. Besides this, the electrochemical response of the sandwich immunosensor (HRP–Ab-Vc/Vc/BSA/Ab-Vc/CH–NiO/ITO) towards H2O2 concentration is found to be linear in the range of 10–50 mM with excellent sensitivity (2.95 mA mM−1 cm−2).

We report results of the studies relating to fabrication of an electrochemical mediator-free biosensor platform using in situ synthesized cadmium sulfide quantum dots (CdS QDs) embedded in chitosan (CHIT) via surface functionalization of cholesterol esterase (ChEt) and cholesterol oxidase (ChOx) enzyme molecules. The results of the microscopic studies of CHIT–CdS QDs biocomposite reveal homogeneous dispersion of the embedded CdS QDs in CHIT and specific combinational symmetry of the S2− rich species CdS QDs, with CHIT and ChOx–ChEt molecules. The electrochemical studies exhibit the enhanced redox activated behavior of ChOx–ChEt molecules which in turn is found to depend on the size of the chitosan capped CdS QDs, facilitating the fast diffusion of electrons from ChOx–ChEt to the electrode surface. The biofunctionalized CHIT–CdS QDs based biosensor platform utilized for the estimation of total cholesterol without using any mediator shows high sensitivity (0.384 μA mM−1 cm−2) in a wide detection range (0.64–12.9 mM) of total cholesterol. This Cds QDs based platform has enormous possibilities for the development of biosensors for clinical diagnostics.