Electrochemical and Plasmonic Detection of Myocardial Infarction Using Microfluidic Biochip Incorporated with Mesoporous Nanoscaffolds.

This paper reports a microfluidic device for the electrochemical and plasmonic detection of cardiac myoglobin (cMb) and cardiac troponin I (cTnI) with noticeable limits of detection (LoD) as low as a few picograms per milliliter (pg/mL) ranges, achieved in a short detection time. The device features two working electrodes, each with a mesoporous Ni3V2O8 nanoscaffold grafted with reduced graphene oxide (rGO) that improves the interaction of diffusing analyte molecules with the sensing surface by providing a high surface area and reaction kinetics. Electrochemical studies reveal sensitivities as high as 9.68 µA ng/mL and a LoD of 2.0 pg/mL for cTnI, and 8.98 µA ng/mL and 4.7 pg/mL for cMb. Additionally, the surface plasmon resonance (SPR) studies demonstrate a low-level LoD of 8.8 pg/mL for cMb and 7.3 pg/mL for cTnI. The dual-modality sensor enables dynamic tracking of kinetic antigen-antibody interactions during sensing, self-verification through providing signals of two modes, and reduced false readout. This study demonstrates the complementary nature of the electrochemical and SPR modes in biosensing, with the electrochemical mode being highly sensitive and the SPR mode providing superior tracking of molecular recognition behaviors. The presented sensor represents a significant innovation in cardiovascular disease management and can be applied to monitor other clinically important biomolecules.

Recent developments in wearable & non-wearable point-of-care biosensors for cortisol detection.

INTRODUCTION: Cortisol is one of the most prominent biomarkers used for the detection of psychological stress and related disorders. It plays an important role in many physiological processes including immunomodulation and fat metabolism. Thus, monitoring of cortisol levels can be used to indicate different pathological conditions including stress disorders. There has been a gradual rise in the development of point of care (PoC) biosensors for continuous cortisol monitoring. AREAS COVERED: This review discusses recent breakthroughs toward the development of PoC sensors (wearable and non wearable) for cortisol monitoring. Challenges associated with them have also been summarized. EXPERT OPINION: Electrochemical PoC devices have recently emerged as a powerful tools for continuous monitoring of cortisol that can be utilized for stress management and treatment of related disorders. However, there are many challenges that should be addressed before such devices can be deployed at mass level, such as inter-individual variability, changing the device calibration with the circadian rhythm, interference from other endocrine moieties, etc. [Figure: see text].

Conductive Ink-Coated Paper-Based Supersandwich DNA Biosensor for Ultrasensitive Detection of Neisseria gonorrhoeae.

Herein, we report results of the studies relating to the development of an impedimetric, magnetic bead-assisted supersandwich DNA hybridization assay for ultrasensitive detection of Neisseria gonorrhoeae, the causative agent of a sexually transmitted infection (STI), gonorrhea. First, a conductive ink was formulated by homogenously dispersing carboxylated multiwalled carbon nanotubes (cMWCNTs) in a stable emulsion of terpineol and an aqueous suspension of carboxymethyl cellulose (CMC). The ink, labeled C5, was coated onto paper substrates to fabricate C5@paper conductive electrodes. Thereafter, a magnetic bead (MB)-assisted supersandwich DNA hybridization assay was optimized against the porA pseudogene of N. gonorrhoeae. For this purpose, a pair of specific 5' aminated capture probes (SCP) and supersandwich detector probes (SDP) was designed, which allowed the enrichment of target gonorrheal DNA sequence from a milieu of substances. The SD probe was designed such that instead of 1:1 binding, it allowed the binding of more than one T strand, leading to a 'ladder-like' DNA supersandwich structure. The MB-assisted supersandwich assay was integrated into the C5@paper electrodes for electrochemical analysis. The C5@paper electrodes were found to be highly conductive by a four-probe conductivity method (maximum conductivity of 10.1 S·cm-1). Further, the biosensing assay displayed a wide linear range of 100 aM-100 nM (109 orders of magnitude) with an excellent sensitivity of 22.6 kΩ·(log[concentration])-1. The clinical applicability of the biosensing assay was assessed by detecting genomic DNA extracted from N. gonorrhoeae in the presence of DNA from different non-gonorrheal bacterial species. In conclusion, this study demonstrates a highly sensitive, cost-effective, and label-free paper-based device for STI diagnostics. The ink formulation prepared for the study was found to be highly thixotropic, which indicates that the paper electrodes can be screen-printed in a reproducible and scalable manner.

Nanopatterned cadmium selenide Langmuir-Blodgett platform for leukemia detection.

We present results of the studies relating to preparation of Langmuir-Blodgett (LB) monolayers of tri-n-octylphosphine oxide-capped cadmium selenide quantum dots (QCdSe) onto indium-tin oxide (ITO) coated glass substrate. The monolayer behavior has been studied at the air-water interface under various subphase conditions. This nanopatterned platform has been explored to fabricate an electrochemical DNA biosensor for detection of chronic myelogenous leukemia (CML) by covalently immobilizing the thiol-terminated oligonucleotide probe sequence via a displacement reaction. The results of electrochemical response studies reveal that this biosensor can detect target DNA in the range of 10(-6) to 10(-14) M within 120 s, has a shelf life of 2 months, and can be used about 8 times. Further, this nucleic acid sensor has been found to distinguish the CML-positive and the control negative clinical patient samples.

Applications of metal-organic framework-based bioelectrodes.

Metal-organic frameworks (MOFs) are an emerging class of porous nanomaterials that have opened new research possibilities. The inherent characteristics of MOFs such as their large surface area, high porosity, tunable pore size, stability, facile synthetic strategies and catalytic nature have made them promising materials for enormous number of applications, including fuel storage, energy conversion, separation, and gas purification. Recently, their high potential as ideal platforms for biomolecule immobilization has been discovered. MOF-enzyme-based materials have attracted the attention of researchers from all fields with the expansion of MOFs development, paving way for the fabrication of bioelectrochemical devices with unique characteristics. MOFs-based bioelectrodes have steadily gained interest, wherein MOFs can be utilized for improved biomolecule immobilization, electrolyte membranes, fuel storage, biocatalysis and biosensing. Likewise, applications of MOFs in point-of-care diagnostics, including self-powered biosensors, are exponentially increasing. This paper reviews the current trends in the fabrication of MOFs-based bioelectrodes with emphasis on their applications in biosensors and biofuel cells.

Electrochemical Immunosensor for Detection of H. pylori Secretory Protein VacA on g-C3N4/ZnO Nanocomposite-Modified Au Electrode.

A g-C3N4/ZnO (graphitic carbon nitride/zinc oxide) nanocomposite-decorated gold electrode was employed to design an antigen-antibody-based electrochemical biosensor to detect Helicobacter pylori specific toxin, vacuolating cytotoxin A (VacA). The thermal condensation method was used to synthesize the g-C3N4/ZnO nanocomposite, and the nanocomposite was deposited electrochemically on a gold electrode. The morphology as well as the structure of the synthesized nanocomposite were confirmed by scanning electron microscopy, energy-dispersive X-ray analysis, X-ray diffraction, and Fourier transform infrared techniques. The nanocomposite efficiently increased the sensor performance by amplifying the signals. EDC-NHS chemistry was exploited for attachment of VacA antibodies covalently with the g-C3N4/ZnO-modified gold electrode. This modified electrode was exploited for immunosensing of H. pylori-specific VacA antigen. The immunosensor was stable for up to 30 days and exhibited good sensitivity of 0.3 µA-1 ng mL-1 in a linear detection range of 0.1 to 12.8 ng mL-1. Apart from this, the fabricated sensor showed unprecedented reproducibility and remarkable selectivity toward the H. pylori toxin VacA. Thus, the highly sensitive immunosensor is a desirable platform for H. pylori detection in practical applications and clinical diagnosis.

Molecularly imprinted polyaniline film for ascorbic acid detection.

Molecularly imprinted polyaniline (PANI) film (∼ 100 nm thick) has been electrochemically fabricated onto indium-tin-oxide (ITO) coated glass plate using ascorbic acid (AA) as template molecule. Fourier transform infra-red spectroscopy, scanning electron microscopy, cyclic voltammetry and differential pulse voltammetry (DPV) studies indicate the presence of AA in PANI matrix, which also acts as a dopant for PANI. Further, the AA selective molecularly imprinted PANI electrode (AA-MI-PANI/ITO) has been developed via over-oxidation of AA doped PANI electrode which leads to the removal of AA moieties from PANI film. The response studies using DPV technique have revealed that this molecularly imprinted AA-MI-PANI/ITO electrode can detect AA in the range of 0.05-0.4 mM with detection limit of 0.018 mM and sensitivity of 1.2 × 10(-5) AmM(-1). Interestingly, this AA-MI-PANI/ITO electrode shows excellent reusability, selectivity and stability.

Microstructured cystine dendrites-based impedimetric sensor for nucleic acid detection.

We report results of the studies relating to the fabrication and characterization of novel biosensing electrode by covalent immobilization of DNA onto microstructural cystine (Cys) prepared by acoustic cavitation method. The TEM investigations of these structures reveal transformation of microstructured Cys from nanorods to dendritic structure under optimum conditions. The Cys dendrites (denCys) have been investigated by XRD, FT-IR, and SEM studies. These biosensing electrodes have been fabricated by immobilization of Escherichia coli (E. coli)-specific DNA probe onto the dendritic cystine. The results of the electrochemical impedance spectroscopy studies reveal that this nucleic acid sensor exhibits linear response to cDNA in the concentration range of 10(-6) to 10(-14) M with response time of 30 min. The biosensing characteristics show that the fabricated E. coli sensor can be reused about 4 times and is stable for ∼4 weeks. The studies on cross-reactivity of the sensor for other water-borne pathogens like Salmonella typhimurium, Neisseria meningitides, and Klebsiella pneumonia reveal specificity of the bioelectrode for E. coli detection.

Emerging DNA-based multifunctional nano-biomaterials towards electrochemical sensing applications.

DNA is known to be ubiquitous in nature as it is the controlling unit for genetic information storage in most living organisms. Lately, there has been a surge in studies relating to the use of DNA as a biomaterial for various biomedical applications such as biosensing, therapeutics, and drug delivery. The role of DNA as a bioreceptor in biosensors has been known for a long time. DNA-based biosensors are gradually evolving into highly sophisticated and sensitive molecular devices. The current realization of DNA-based biosensors embraces the unique structural and functional properties of DNA in the form of a biopolymer. The interesting properties of DNA, such as self-assembly, programmability, catalytic activity, dynamic behavior, and precise molecular recognition, have led to the emergence of innovative DNA assembly based electrochemical biosensors. This review article aims to cover the recent progress in the field of DNA-based electrochemical (EC) biosensors. It commences with an introduction to electrochemical biosensors and elucidates the advantages of integrating DNA-based materials into them. Besides this, we discuss the principles of EC biosensors based on different types of DNA-based materials. The article concludes by highlighting the outlook and importance of this interesting field for biomedical developments.

Ultrasensitive biosensing platform based on yttria doped zirconia-reduced graphene oxide nanocomposite for detection of salivary oral cancer biomarker.

Herein, we report results of the studies relating to the fabrication of yttria-doped zirconia-reduced graphene oxide nanocomposite (nYZR) based biosensing platform for detection of salivary CYFRA-21-1 biomarker. The nYZR nanocomposite was hydrothermally synthesized and amine-functionalized using 3-aminopropyl triethoxysilane (APTES). This functionalized nanocomposite (APTES/nYZR) was electrophoretically deposited (45 V; 3 min) onto pre-hydrolyzed indium tin oxide (ITO) coated glass substrate (APTES/nYZR/ITO) followed by biofunctionalization via covalent immobilization of the anti-CYFRA-21-1 antibodies (anti-CYFRA-21-1/APTES/nYZR/ITO). The synthesized nanomaterial and the fabricated electrodes were characterized to investigate crystal structure, morphology and electrochemical properties via X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, cyclic voltammetry, differential pulse voltammetry and electrochemical impedance spectroscopy. The fabricated biosensing electrode (BSA/anti-CYFRA-21-1/APTES/nYZR/ITO) has an operating shelf life of 56 days and can be used to detect salivary CYFRA-21-1 biomarker concentration as low as 7.2 pg mL-1 with wide linear detection range of 0.01-50 ng mL-1. This work opens new opportunities to explore the electrochemical behavior of nanostructured yttria stabilized zirconia (YSZ) and its composites at room temperature and its utility in developing biosensors and other electrochemical devices.

Prospects of nanomaterials-enabled biosensors for COVID-19 detection.

We are currently facing the COVID-19 pandemic which is the consequence of severe acute respiratory syndrome coronavirus (SARS-CoV-2). Since no specific vaccines or drugs have been developed till date for the treatment of SARS-CoV-2 infection, early diagnosis is essential to further combat this pandemic. In this context, the reliable, rapid, and low-cost technique for SARS-CoV-2 diagnosis is the foremost priority. At present reverse transcription polymerase chain reaction (RT-PCR) is the reference technique presently being used for the detection of SARS-CoV-2 infection. However, in a number of cases, false results have been noticed in COVID-19 diagnosis. To develop advanced techniques, researchers are continuously working and in the series of constant efforts, nanomaterials-enabled biosensing approaches can be a hope to offer novel techniques that may perhaps meet the current demand of fast and early diagnosis of COVID-19 cases. This paper provides an overview of the COVID-19 pandemic and nanomaterials-enabled biosensing approaches that have been recently reported for the diagnosis of SARS-CoV-2. Though limited studies on the development of nanomaterials enabled biosensing techniques for the diagnosis of SARS-CoV-2 have been reported, this review summarizes nanomaterials mediated improved biosensing strategies and the possible mechanisms that may be responsible for the diagnosis of the COVID-19 disease. It is reviewed that nanomaterials e.g. gold nanostructures, lanthanide-doped polysterene nanoparticles (NPs), graphene and iron oxide NPs can be potentially used to develop advanced techniques offered by colorimetric, amperometric, impedimetric, fluorescence, and optomagnetic based biosensing of SARS-CoV-2. Finally, critical issues that are likely to accelerate the development of nanomaterials-enabled biosensing for SARS-CoV-2 infection have been discussed in detail. This review may serve as a guide for the development of advanced techniques for nanomaterials enabled biosensing to fulfill the present demand of low-cost, rapid and early diagnosis of COVID-19 infection.

Point-of-Care PCR Assays for COVID-19 Detection.

Molecular diagnostics has been the front runner in the world's response to the COVID-19 pandemic. Particularly, reverse transcriptase-polymerase chain reaction (RT-PCR) and the quantitative variant (qRT-PCR) have been the gold standard for COVID-19 diagnosis. However, faster antigen tests and other point-of-care (POC) devices have also played a significant role in containing the spread of SARS-CoV-2 by facilitating mass screening and delivering results in less time. Thus, despite the higher sensitivity and specificity of the RT-PCR assays, the impact of POC tests cannot be ignored. As a consequence, there has been an increased interest in the development of miniaturized, high-throughput, and automated PCR systems, many of which can be used at point-of-care. This review summarizes the recent advances in the development of miniaturized PCR systems with an emphasis on COVID-19 detection. The distinct features of digital PCR and electrochemical PCR are detailed along with the challenges. The potential of CRISPR/Cas technology for POC diagnostics is also highlighted. Commercial RT-PCR POC systems approved by various agencies for COVID-19 detection are discussed.

Gold nanomaterials for optical biosensing and bioimaging.

Gold nanoparticles (AuNPs) are highly compelling nanomaterials for biomedical studies due to their unique optical properties. By leveraging the versatile optical properties of different gold nanostructures, the performance of biosensing and biomedical imaging can be dramatically improved in terms of their sensitivity, specificity, speed, contrast, resolution and penetration depth. Here we review recent advances of optical biosensing and bioimaging techniques based on three major optical properties of AuNPs: surface plasmon resonance, surface enhanced Raman scattering and luminescence. We summarize the fabrication methods and optical properties of different types of AuNPs, highlight the emerging applications of these AuNPs for novel optical biosensors and biomedical imaging innovations, and discuss the future trends of AuNP-based optical biosensors and bioimaging as well as the challenges of implementing these techniques in preclinical and clinical investigations.

Electrophoretically deposited polyaniline nanotubes based film for cholesterol detection.

Polyaniline nanotube (PANI-NT) based films have been fabricated onto indium-tin-oxide (ITO) coated glass plates via electrophoretic technique. These PANI-NT/ITO electrodes have been utilized for covalent immobilization of cholesterol oxidase (ChOx) using glutaraldehyde (Glu) as cross-linker. Structural, morphological and electrochemical characterization of PANI-NT/ITO electrode and ChOx/Glu/PANI-NT/ITO bioelectrode have been done using FT-IR spectroscopy, SEM, electrochemical impedance spectroscopy and cyclic voltammetry techniques. Response studies of the ChOx/Glu/PANI-NT/ITO bioelectrode have been carried out using both linear sweep voltammetry and UV-Visible spectrophotometry. The results of the biosensing studies reveal that this bioelectrode can be used to detect cholesterol in wide detection range of 25-500 mg/dL with high sensitivity of 3.36 mA mg(-1) dL and fast response time of 30 s at pH 7.4. This bioelectrode exhibits very low value of Michaelis-Menten constant of 1.18 mM indicating enhanced interactions between cholesterol and ChOx immobilized onto this nanostructured PANI matrix.

Nanostructured conducting polymer based reagentless capacitive immunosensor.

Nanostructured polyaniline (PANI) film electrophoretically fabricated onto indium-tin-oxide (ITO) coated glass plate has been utilized for development of an immunosensor based on capacitance change of a parallel plate capacitor (PPC) by covalently immobilizing anti-human IgG (Anti-HIgG) using N-ethyl-N'-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide chemistry. These fabricated PANI/ITO and Anti-HIgG/PANI/ITO plates have been characterized using scanning electron microscopy, cyclic voltammetry, differential pulse voltammetry and Fourier transform infra-red studies. The capacitance measurements indicate that dielectric medium of this biologically modified PPC (Anti-HIgG/PANI/ITO) is sensitive to HIgG in 5 - 5 x 10(5) ng mL(-1) range and has lower detection limit of 1.87 ng mL(-1). The observed results reveal that this Anti-HIgG modified PPC can be used as a robust, easy-to-use, reagentless, sensitive and selective immunosensor for estimation of human IgG.

Recent Advances of Conducting Polymers and Their Composites for Electrochemical Biosensing Applications.

Conducting polymers (CPs) have been at the center of research owing to their metal-like electrochemical properties and polymer-like dispersion nature. CPs and their composites serve as ideal functional materials for diversified biomedical applications like drug delivery, tissue engineering, and diagnostics. There have also been numerous biosensing platforms based on polyaniline (PANI), polypyrrole (PPY), polythiophene (PTP), and their composites. Based on their unique properties and extensive use in biosensing matrices, updated information on novel CPs and their role is appealing. This review focuses on the properties and performance of biosensing matrices based on CPs reported in the last three years. The salient features of CPs like PANI, PPY, PTP, and their composites with nanoparticles, carbon materials, etc. are outlined along with respective examples. A description of mediator conjugated biosensor designs and enzymeless CPs based glucose sensing has also been included. The future research trends with required improvements to improve the analytical performance of CP-biosensing devices have also been addressed.

Emerging Trends in Microfluidics Based Devices.

One of the major challenges for scientists and engineers today is to develop technologies for the improvement of human health in both developed and developing countries. However, the need for cost-effective, high-performance diagnostic techniques is very crucial for providing accessible, affordable, and high-quality healthcare devices. In this context, microfluidic-based devices (MFDs) offer powerful platforms for automation and integration of complex tasks onto a single chip. The distinct advantage of MFDs lies in precise control of the sample quantities and flow rate of samples and reagents that enable quantification and detection of analytes with high resolution and sensitivity. With these excellent properties, microfluidics (MFs) have been used for various applications in healthcare, along with other biological and medical areas. This review focuses on the emerging demands of MFs in different fields such as biomedical diagnostics, environmental analysis, food and agriculture research, etc., in the last three or so years. It also aims to reveal new opportunities in these areas and future prospects of commercial MFDs.

Amine-Functionalized MoO3@RGO Nanohybrid-Based Biosensor for Breast Cancer Detection.

We report results of studies relating to development of an ultrasensitive, rapid, and label-free biosensor based on molybdenum trioxide (MoO3) anchored onto the reduced graphene oxide (RGO) for breast cancer detection. The human epidermal growth factor receptor-2 (HER-2) secreted in the serum of breast cancer patients was used as an analyte for the detection. The in situ growth of 1D MoO3 onto reduced graphene oxide (RGO), a 2D carbon substrate, was carried out via one-pot low-temperature hydrothermal synthesis. Subsequently, the surface conjugation of the monoclonal antibodies (anti-HER-2) onto the APTES/MoO3@RGO/ITO electrode was conducted via EDC-NHS covalent chemistry. The structural and morphological properties of the MoO3@RGO nanohybrid were investigated using electron microscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopic techniques. The surface area of the MoO3@RGO nanohybrid determined via Brauner-Emmett-Teller analysis was found to be 14 times greater than that of the pristine MoO3. The binding kinetics and the electrochemical activity of the developed platform were determined by cyclic voltammetry, differential pulse voltammetry, and impedance spectroscopic techniques. This nanohybrid based immunosensor exhibited improved sensitivity (13 uA mLng-1cm-2) in a broad concentration range (0.001-500 ng mL-1) with a correlation coefficient of 0.98. The limit of detection of this MoO3@RGO nanohybrid based immunosensor was found to be 0.001 ng mL-1. The results obtained via the developed immunosensor for the quantification of serum HER-2 were validated using ELISA.

Nanomaterial-Modified Conducting Paper: Fabrication, Properties, and Emerging Biomedical Applications.

The emerging demand for wearable, lightweight portable devices has led to the development of new materials for flexible electronics using non-rigid substrates. In this context, nanomaterial-modified conducting paper (CP) represents a new concept that utilizes paper as a functional part in various devices. Paper has drawn significant interest among the research community because it is ubiquitous, cheap, and environmentally friendly. This review provides information on the basic characteristics of paper and its functionalization with nanomaterials, methodology for device fabrication, and their various applications. It also highlights some of the exciting applications of CP in point-of-care diagnostics for biomedical applications. Furthermore, recent challenges and opportunities in paper-based devices are summarized.

Protein functionalised self assembled monolayer based biosensor for colon cancer detection.

We report results of the studies relating to the fabrication of a surface plasmon resonance (SPR) based label-free immunosensor for real-time monitoring of endothelin-1 (ET-1), a colon cancer biomarker. A gold disk modified with a self-assembled monolayer (SAM) of 11-mercaptoundecanoic acid (11-MUA) was functionalised via covalent immobilization of monoclonal anti-ET-1 antibodies using EDC-NHS (1-(3-(dimethylamine)-propyl)-3-ethylcarbodiimide hydrochloride, N-hydroxy succinimide) chemistry. This immunosensing platform (ethanolamine/anti-ET-1/11-MUA/Au) was characterized via atomic force microscopy (AFM), contact angle (CA) and Fourier transform infrared (FT-IR) spectroscopic techniques. The fabricated SPR electrode was further used to detect ET-1 in the broad concentration range 2-100 pg mL-1, with a detection limit of 0.30 pg mL-1 and remarkable sensitivity of 2.18 mo pg-1mL. The adsorption mechanism was studied using monophasic model and the values of association (ka) and dissociation (kd) constants for anti-ET-1 and ET-1 binding were calculated to be 4.4 ±â€¯0.4 × 105 M-1 s-1 and 2.04 ±â€¯0.0003 × 10-3 s-1, respectively. The results obtained via analysis of serum samples of colorectal cancer patients were found to be in good agreement with those obtained from enzyme-linked immunosorbent assay (ELISA) technique. Further, electrochemical studies were performed to prove the efficacy of the fabricated platform as a point of care device for the detection of ET-1.