Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2, also known as 2019-nCov or nCovid-19) outbreak has become a huge public health issue due to its rapid transmission making it a global pandemic. Currently, there are no vaccines or drugs available for nCovid-19, hence early detection is crucial to help and manage the outbreak. Here, we report an inhouse built biosensor device (eCovSens) and compare it with a commercial potentiostat machine for the detection of nCovid-19 spike protein antigen (nCovid-19 Ag) in spiked saliva samples. A potentiostat based sensor was fabricated using fluorine doped tin oxide electrode (FTO) drop casted with gold nanoparticle (AuNPs) and immobilized with nCovid-19 monoclonal antibody (nCovid-19 Ab) to measure change in the electrical conductivity. Similarly, eCovSens was used to measure change in electrical conductivity by immobilizing nCovid-19 Ab on screen printed carbon electrode (SPCE). The performances of both sensors were recorded upon interaction of nCovid-19 Ab with its specific nCovid-19 Ag. Under optimum conditions, the FTO based immunosensor and proposed SPCE-based biosensor device displayed high sensitivity for early detection of nCovid-19 Ag, ranging from 1 fM to 1 µM. Our in-house developed eCovSens device can successfully detect nCovid-19 Ag at 10 fM concentration in standard buffer that is in close agreement with FTO/AuNPs sensor where AuNPs were used for the amplification of the electrical signal. The limit of detection (LOD) was found to be 90 fM with eCovSens and 120 fM with potentiostst in case of spiked saliva samples. The proposed portable point of care (PoC) eCovSens device can be used as an alternative diagnostic tool for the rapid (within 10-30 s) detection of nCovid-19 Ag traces directly in patient saliva samples that displayed high sensitivity, stability, and specificity.

Graphene, a two-dimensional nanomaterial, has gained immense interest in biosensing applications due to its large surface-to-volume ratio, and excellent electrical properties. Herein, a compact and user-friendly graphene field effect transistor (GraFET) based ultrasensitive biosensor has been developed for detecting Japanese Encephalitis Virus (JEV) and Avian Influenza Virus (AIV). The novel sensing platform comprised of carboxy functionalized graphene on Si/SiO 2 substrate for covalent immobilization of monoclonal antibodies of JEV and AIV. The bioconjugation and fabrication process of GraFET was characterized by various biophysical techniques such as Ultraviolet-Visible (UV-Vis), Raman, Fourier-Transform Infrared (FT-IR) spectroscopy, optical microscopy, Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The change in the resistance due to antigenantibody interaction was monitored in real time to evaluate the electrical response of the sensors. The sensors were tested in the range of 1 fM to 1 μM for both JEV and AIV antigens, and showed a limit of detection (LOD) upto 1 fM and 10 fM for JEV and AIV respectively under optimised conditions. Along with ease of fabrication, the GraFET devices were highly sensitive, specific, reproducible, and capable of detecting ultralow levels of JEV and AIV antigen. Moreover, these devices can be easily integrated into miniaturized FET-based real-time sensors for the rapid, cost-effective, and early Point of Care (PoC) diagnosis of JEV and AIV. The development of Point of Care (PoC) disease detection kits providing ultra-sensitive, selective, and rapid advances in recent times. In this article, we have focused on graphene-based biosensors for the detection of two different viruses by detecting their respective viral antigen i.e. Japanese encephalitis virus (JEV) and Avian Influenza Virus (AIV). JEV belongs to the family Flaviviridae genus Flavivirus 1 and exists in a zoonotic cycle between the vector i.e. Culex mosquitos, while humans are the dead end host due to low and short-lived viremia of JEV 2-5. Most infections of JEV are asymptomatic, however, the case-fatality rate among those with encephalitis can be as high as 30%, or more in children. It causes clinical symptoms in humans, including a non-specific febrile illness, meningitis, encephalitis and meningo-encephalitis. Pigs play an important role and serve as an amplifier and have a natural infection rate of 98-100% 6. As JEV is incurable and the vaccination is not full-proof, an early diagnosis is critical in preventing an epidemic outbreak, especially since the initial symptoms are usually mistaken for dengue or malaria. The conventional diagnostic methods for JEV 7 such as Enzyme-Linked Immunosorbent Assays (ELISA) 8 ,

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2, also known as 2019-nCov or COVID-19) outbreak has become a huge public health issue due to its rapid transmission making it a global pandemic. Here, we report fabricated fluorine doped tin oxide (FTO) electrodes/gold nanoparticles (AuNPs) complex coupled with in-house developed SARS-CoV-2 spike S1 antibody (SARS-CoV-2 Ab) to measure the response with Cyclic Voltammetry (CV) and Differential Pulse Voltammetry (DPV). The biophysical characterisation of FTO/AuNPs/SARS-CoV-2Ab was done via UV-Visible spectroscopy, Dynamic Light Scattering (DLS), and Fourier Transform Infrared Spectroscopy (FT-IR). The fabricated FTO/AuNPs/SARS-CoV-2Ab immunosensor was optimised for response time, antibody concentration, temperature, and pH. Under optimum conditions, the FTO/AuNPs/Ab based immunosensor displayed high sensitivity with limit of detection (LOD) up to 0.63 fM in in standard buffer and 120 fM in spiked saliva samples for detection of SARS-CoV-2 spike S1 antigen (Ag) with negligible cross reactivity Middle East Respiratory Syndrome (MERS) spike protein. The proposed FTO/AuNPs/SARS-CoV-2Ab based biosensor proved to be stable for up to 4 weeks and can be used as an alternative non-invasive diagnostic tool for the rapid, specific and sensitive detection of SARS-CoV-2 Spike Ag traces in clinical samples.

This study describes the colorimetric detection of aflatoxin M1 (Afl M1) in milk samples using a microfluidic paper-based analytical device (µPAD). Fabrication of µPADs was done using a simple and quick approach. Each μPAD contained a detection zone and a sample zone interconnected by microchannels. The colorimetric assay was developed using unmodified AuNPs as a probe and 21-mer aptamer as a recognition molecule. The free aptamers were adsorbed onto the surface of AuNPs in absence of Afl M1, even at high salt concentrations. The salt induced aggregation of specific aptamers occurred in presence of Afl M1. Under optimum conditions, the analytical linear range was found to be 1 µM to 1 pM with limit of detection 3 pM and 10 nM in standard buffer and spiked milk samples respectively. The proposed aptamer based colorimetric assay was repeatable, quick, selective, and can be used for on-site detection of other toxins in milk and meat samples. Mycotoxins are secondary metabolites produced by filamentous fungi belonging to the genera Aspergillus and Penicillium 1. Mycotoxins are also found in animal derived foods such as milk due to intake of contaminated feed 2,3. Considering agricultural and economical aspects and possible implications on public health, the most relevant mycotoxins are aflatoxins, ochratoxins, fuminosins, T-2 toxin, and zearalenone (ZEA) 4. Aflatoxins pose a huge economic burden as they cause around 25% or more loss of the world's food crops every year 5. Afl M1 (4-hydroxy aflatoxin B1) and M2 (4-dihydroxy aflatoxin B1) have well proven carcinogenic and mutagenic potentiality and pose severe health consequences on milk consumers, including the risk of cancer and stunted growth in children below the age of 5 years 6. When B1 is ingested by a cow, it is secreted as hydroxylated metabolite aflatoxin M1 (Afl M1) in the urine and milk of the cow 7. Consumption of food containing aflatoxin concentrations of one milligram/kilogram or higher has been suspected to cause aflatoxicosis 8 , the prognosis of which consists of acute liver failure, jaundice, lethargy, and nausea, eventually leading to death within 1 to 2 weeks, based on past reports 9. Thus there is a need to develop rapid low cost technology based highly specific methods for detection of aflatoxins to improve surveillance and control in rural areas. A plethora of analytical techniques are available for aflatoxin M1 detection, ranging from chromatography and HPLC-MS used for regulatory control in official laboratories to rapid test kits for grain silos and farmers, especially for surveys when outbreaks occur 10,11. Conventional techniques for the detection of aflatoxins include gas chromatography (GC), fluorescence or UV based detection, thin layer chromatography (TLC) and enzyme linked immunosorbent assay (ELISA) 6-12. These techniques are routinely used and yield reliable results, however they are expensive, time consuming, require large scale instrumentation and large amounts of hazardous chemical reagents. Advancement in the development of bios...

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