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A paper-based colourimetric assay for the Point-of-Care Testing (PoCT) of bilirubin has been developed based on the formation of a green-coloured copper-bilirubin complex from a blue-coloured tetraamminecopper(II) sulphate complex. The reaction was studied and optimized by UV-Visible absorption spectroscopy and translated onto a paper strip. Hydrophobic circular well patterns on Whatman chromatography paper were created by wax printing. The tetraamminecopper(II) sulphate complex was drop cast and dried on the reagent zones in the wax-patterned paper. The images of reagent zones captured using a scanner were analyzed using ImageJ software. Bilirubin spiked blood serum was tested in the concentration range of 1.2 to 950 µM. The PAD exhibited sensitivities of 0.4197 a.u/μM and 0.1040 a.u/μM for concentration ranges of bilirubin 1.2 to 96 μM and 105 to 950 μM respectively and a low detection limit of 0.799 µM. The method is highly selective to bilirubin, even in the presence of other biomarkers in serum. A plasma separation membrane incorporated PAD was fabricated for the final testing and quantification of bilirubin from whole blood.

This paper reports the development and fabrication of a low-cost handheld point of care device that can quantify the concentration of biomarkers using a paper microfluidic assay. The commercially available light-to-digital converting sensor was used to achieve this objective. This RGB sensor was efficient in the digital values of the red, green, and blue components of the sample or object. It has an inbuilt white LED source, an array of photodiodes with color filters, an analog-to-digital converter module, and also an IR blocking filter. The sensor was interfaced with the Arduino UNO board, and the corresponding results were displayed on the serial monitor. This device was tested for manually prepared primary color samples and also for total protein. The colorimetric detection of protein was performed for 1 g dL-1 to 14 g dL-1 concentrations on a paper microfluidic device. The change in color intensity of the paper device with an increase in total protein concentration was monitored and calibrated the device for real sample analysis.

In this paper, we report a wet chemical synthesis of polyaniline – platinum nanocomposite and the fabrication of a flexible supercapacitor. Capacitive properties of the synthesized materials were analyzed using cyclic voltammetry, EIS, and galvanostatic charge–discharge. The high areal capacitance of 102 mF cm−2 was obtained for polyaniline platinum nanocomposite with 10 wt% graphite and 10 wt% PTFE binder. The prototype of a parallel plate supercapacitor was fabricated with an optimum concentration of HCl incorporated cellulose paper as the dielectric medium. Polyaniline –platinum composite exhibited high specific capacitance of 280F g−1, with characteristic breakdown potential of 1.0 V, a specific energy density of 2.46 W h g−1, and a specific power density of 0.15 W g−1. It also exhibits high elasticity and flexibility. The capacitance is not altered while applying strain which indicates the applicability of polyaniline and its nanocomposites for flexible electronics.

Electrochemical energy sources especially rechargeable batteries hold a great promise for meeting the ever-growing demand for energy. Though lead acid and lithium ion batteries have been highly successful commercially, the safety issues in using them have led to the development of alternate rechargeable systems. In this regard, silver peroxide-zinc rechargeable batteries are of great importance especially as energy sources for biomedical devices as they can be tuned to obtain low power discharge over prolonged time duration. This study focuses on the electrochemical synthesis of silver peroxide on silver electrodes and its use as the cathode for rechargeable battery. Synthesis parameters were optimized for the formation of silver peroxide and the oxide thus formed was characterized using XRD, EDS, IR spectroscopy, FESEM and AFM. Two different prototypes of batteries (two compartment and pouch model) were fabricated using zinc as the anode and silver peroxide as cathode. The prototypes were able to provide potential of 1.5 V with a power rating of 150 µW and 3.3 µW for the two compartments and pouch model respectively. Both the models were rechargeable and are having low internal resistance

Reduced graphene oxide modified with gold nanoparticles (Au/rGO) was synthesized and used for nonenzymatic electrochemical detection of glucose in a neutral medium. Graphene oxide (GO) was synthesized by modified Hummer's method. Electrocatalyst Au/rGO nanocomposite was synthesized by the simultaneous reduction of gold ions and graphene oxide in a one-pot wet chemical method. Spectroscopic, morphological, and elemental characterizations confirmed the presence of gold nanoparticles (AuNPs) on the surface of reduced graphene oxide. The characteristic surface plasmon resonance band of Au nanoparticle was observed at 540 nm in the composite. The Au/rGO nanocomposite was dispersed in DMF and cast on the screen-printed carbon electrode. The Au/rGO modified electrode was found to catalyze the electrooxidation of glucose in a neutral medium. The sensor exhibited a linear increase in current response with an increase in the concentration of glucose up to 60 mM and a sensitivity of 245 µA mM−1 cm−2. The wide linear range, good sensitivity, and capability to oxidize glucose at neutral pH make the Au/rGO nanocomposite modified electrode a promising candidate for the sensing of glucose in real-time.

In this article, Nitrogen-doped carbon dots (NCDs) were used as a fluorescent probe for the detection of total serum proteins. NCDs were synthesized by microwave-assisted method using citric acid as the carbon source and ethylenediamine as passivating agent. The strong intensity of fluorescence emission was observed at λex/λem ≈ 350/460 nm. The particles are found to be uniformly spherical with an average dimension of 10 nm. The fluorescence intensity of NCDs increased linearly with the addition of bovine serum albumin (BSA) concentrations from 0.5 g/dL to 15 g/dL. The role of interfering agents was investigated and found that NCDs were sensitive to BSA specifically.

The evident spike in the mortality caused due to liver disorders such as liver cirrhosis raised an urgent need for rapid and accurate diagnosis of the disease. Recently, fluorescent carbon dots emerged as an excellent platform for rapid testing in biomedical research. In this work, carbon dots were synthesized by the facile one-step microwave-assisted process by using starch and 50X TAE buffer as the precursors. The synthesized novel nitrogen-doped carbon dots (NCD) exhibited bright blue color fluorescence under the UV lamp. The photoluminescence emission intensity peak was found to be maximum at 440 nm under an excitation wavelength of 350 nm (λex/λem ∼ 350/440 nm). The quantum yield of NCD was calculated as 53%. The microscopic analysis of NCD showed a uniformly spherical carbon dots with an average hydrodynamic diameter measured as 2.8 ± 0.8 nm. The synthesized NCD has been deployed for the detection of oxaloacetate as a biomarker for estimating the level of aspartate transaminase directly or indirectly in liver disorder. The PL emission response of NCD enhances as the concentration of oxaloacetate increases. The role of interfering agents such as Bilirubin (BR), Uric acid (UA), Ascorbic acid (AA), Glucose (Glu), and many more were tested against a similar concentration of oxaloacetate biomarker. The study revealed the higher selectivity of NCD towards oxaloacetate in the presence of several interfering molecules.

In India, multidrug resistance determinants are much more abundant in community-associated bacterial pathogens due to the improper treatment of domestic and industrial effluents. In particular, a high bacterial load of the opportunistic pathogen P. aeruginosa in sewage and water bodies in India is well documented., Multidrug-resistant community-acquired infections caused by the opportunistic human pathogen Pseudomonas aeruginosa are increasingly reported in India and other locations globally. Since this organism is ubiquitous in the environment, samples such as sewage and wastewater are rich reservoirs of P. aeruginosa bacteriophages. In this study, we report the isolation and characterization of a novel P. aeruginosa N4-like lytic bacteriophage, vB_Pae_AM.P2 (AM.P2), from wastewater in Kerala, India. AM.P2 is a double-stranded DNA podovirus that efficiently lyses the model strain, PAO1, at a multiplicity of infection as low as 0.1 phage per bacterium and resistance frequency of 6.59 × 10−4. Synergy in bactericidal activity was observed between AM.P2 and subinhibitory concentrations of the antibiotic ciprofloxacin. Genome sequencing of AM.P2 revealed features similar to those of the N4-like P. aeruginosa phages LUZ7 and KPP21. As judged by two independent assay methods, spot tests and growth inhibition, AM.P2 successfully inhibited the growth of almost 30% of strains from a contemporary collection of multidrug-resistant P. aeruginosa clinical isolates from South India. Thus, AM.P2 may represent an intriguing candidate for inclusion in bacteriophage cocktails developed for various applications, including water decontamination and clinical bacteriophage therapy. IMPORTANCE In India, multidrug resistance determinants are much more abundant in community-associated bacterial pathogens due to the improper treatment of domestic and industrial effluents. In particular, a high bacterial load of the opportunistic pathogen P. aeruginosa in sewage and water bodies in India is well documented. The isolation and characterization of bacteriophages that could target emerging P. aeruginosa strains, representing possible epicenters for community-acquired infections, could serve as a useful alternative tool for various applications, such as phage therapy and environmental treatment. Continuing to supplement the repertoire of broad-spectrum bacteriophages is an essential tool in confronting this problem.

Much advancement in biological studies has led to the greater understanding of pathological conditions, their diagnosis and treatment modalities. One among them is polymerase chain reaction (PCR) an effective and inexpensive method used in molecular biology for deoxyribose nucleic acid (DNA) amplification. DNA quantification and characterisation is an important step in molecular cloning. Common laboratory techniques like absorption spectrophotometry, spectrofluorometry and real time PCR are used to quantify DNA. Spectrofluorometry is more specific and sensitive than spectrophotometry method. Fluorescence spectroscopy can be used by adding probes to the sample, called fluorescence probing technique. In the present work, animal DNA is extracted from liver tissues initially. The isolated DNA is then treated with certain fluorescence probe, such as methylene blue (MB). This probe can intercalate with DNA conformations and also can be used for quantification of DNA. The interaction studies of MB with DNA gives understanding of the nano-environment of the conformations of DNA. Molecular mechanics calculations are carried out to ascertain the findings from the experimental data.

Protein denaturation occurs when the secondary and tertiary structures of protein undergo conformational changes and native state of protein is destroyed. The most common observation of the denaturation phenomenon is either coagulation or precipitation of proteins. Since the denaturation processes are not strong enough to break the peptide bonds, the amino acid sequence is not perturbed and hence the primary structure of proteins is not affected and uncoils itself into a random shape. There are variety of reagents and conditions which can protein denaturation, such as urea, temperature, pH, alcohol, heavy metal, etc. Heavy metal salts present in the vicinity of a protein can induce protein denaturation by disturbing the disulfide bond. Heavy metal salts which induce protein denaturation are usually Hg2+, Pb2+, Ag+, Tl+, Cd2+ and other metal ions with high atomic weights. The heavy metal salts usually reacts with a protein forming insoluble metal-protein salt. Salts such as silver nitrate are used to prevent gonorrhea infections in the eyes of new born infants. It is also used in treatment of various infection and wounds. The current work will involve the fluorescence spectroscopic studies on protein denaturation induced by heavy metal salts; as reported by the fluorescence probing technique. For this study, we will use bovine serum albumin (BSA) is chosen as the protein. The fluorescent property of Tryptophan (Trp) moiety of BSA can be utilized for the study. It can be understood that in present of silver salt, there is Trp fluorescence quenching and data reveals the denaturation of BSA.

In this paper, we report the design and development of easy-to-fabricate, low cost electromagnetically actuated ON/OFF valves to control multiple fluids on a programmable microfluidics platform. The valves were fabricated using mild steel pieces glued onto a PDMS membrane and its deflection was effected by using an array of solenoids. The activation of solenoid array was controlled using a programmed microcontroller. Numerical studies were carried out to optimize design parameters such as the distance between the valve and the solenoid, membrane thickness and the diameter of the deflection zone. The deflection of the valves was also studied using a high-speed digital camera and the results were in good conformity with the simulation results. Deflections up to 1200 μm could be achieved with a response of 3 ms. The efficiency of the developed platform for controlling multiple fluids was verified by experimental studies using coloured solutions and biosensors.

Disposable screen printed carbon electrodes have been developed for the quantitative determination of free bilirubin. The electrodes were fabricated using graphite carbon ink and characterized with microscopy, spectroscopy and diffraction studies. The carbon ink for printing is made of graphite nanoparticles of size around 50 nm. Electrochemical oxidation of bilirubin was carried out voltammetrically in Trizma buffer of pH 8.5. The sensor showed a dynamic detection range of 5–600 μM and a sensitivity of 95 μAμM−1 cm−2. The SPCE showed superior performance than many of the reported sensors in terms of dynamic range, sensitivity and oxidation potential. Molecules such as ascorbic acid, uric acid, dopamine, glucose, creatinine and ethanol were tested using SPCE and found to be non interfering with the detection of creatinine in the physiological conditions. The sensor was tested using bilirubin spiked serum samples and found that it is giving response to free bilirubin. The sensor was also used to study the affinity of free bilirubin to albumin and displacement of bilirubin from albumin by ibuprofen.

A highly sensitive nonenzymatic hydrogen peroxide (H2O2) sensor was fabricated using platinum nanoparticles decorated reduced graphene oxide (Pt/rGO) nanocomposite. The Pt/rGO nanocomposite was prepared by single-step chemical reduction method. Nanocomposite was characterized by various analytical techniques including Raman spectroscopy, X-ray diffraction, field emission scanning electron microscope and high-resolution transmission electron microscopy. Screen printed electrodes (SPEs) were fabricated and the nanocomposite was cast on the working area of the SPE. Cyclic voltammetry and amperometry demonstrated that the Pt/rGO/SPE displayed much higher electrocatalytic activity towards the reduction of H2O2 than the other modified electrodes. The sensor exhibited wide linear detection range (from 10 μM to 8 mM), very high sensitivity of 1848 μA mM-1 cm-2 and a lower limit of detection of 0.06 μM. The excellent performance of Pt/rGO/SPE sensor were attributed to the reduced graphene oxide being used as an effective matrix to load a number of Pt nanoparticles and the synergistic amplification effect of the two kinds of nanomaterials. Moreover, the sensor showed remarkable features such as good reproducibility, repeatability, long-term stability, and selectivity.

N1,N5-bis(pyridin-2-ylmethylene)naphthalene-1,5-diamine (L1) Schiff base conjugate was synthesized by the condensation reaction of 1,5-diamino naphthalene (1,5-DAN) and 2-pyridine carboxaldehyde and spectroscopically evidenced by 1H NMR, 13C NMR and Mass spectrum. The developed Schiff base conjugate was used as a fluorescent chemosensor for the selective recognition of bismuth (Bi3+) ions in the midst of various interfering heavy transition metal ions such as Ag+, Hg2+ and Cu2+ with marked fluorescence enhancement. Based on “switch-on” intramolecular charge transfer (ICT) approach, chemosensor L1 showed specific response towards bismuth ions with a low detection limit of 1.5 × 10−8 M and a high binding constant 7.11 × 105 M−1. Simultaneously, the experimental (Job’s plot, Mass spectrum, and FT-IR) and theoretical (B3LYP-D3/6–311++G(d,p)) analysis were performed for promising the 1:1 binding mode of L1 + Bi3+ complex formation. The chemosensor L1 has been successfully demonstrated in practical applications such as water and food samples, bacterial imaging and logic gate operation producing satisfactory results.

A paper-based colourimetric assay for the detection of alanine transaminase has been developed. In the presence of alanine transaminase, 2,4-dinitrophenyl hydrazine changes to pyruvate hydrazone leading to a colour change from pale yellow to dark yellow. Reaction conditions were optimized using absorption spectroscopic studies. Hydrophobic patterns on the Whatman chromatographic paper were created by wax printing, and the reagents were drop cast at the reagent zone. On the paper device, the intensity of the yellow colour increases with ALT concentration in the range of 20-140 U/L in human serum. For the quantification of ALT, coloured images were captured using a digital camera and were processed with Image J software. The machine learning approach was also explored for the ALT analysis by training with colour images of the paper device and testing using a cross-validation procedure. The results obtained with real clinical samples on the paper device showed good accuracy of less than 5% relative error with the clinical lab results. Furthermore, the paper device shows high selectivity to ALT in the presence of various interfering species in blood serum with a sensitivity of 0.261 a.u/(U/L), a detection limit of 4.12 U/L, and precise results with an RSD of less than 7%. For the testing of whole blood, a plasma separation membrane was integrated with the patterned paper.

Here, we report cysteamine derived nitrogen and sulfur co-doped carbon dots (Cy@CD) for imaging pathogenic bacteria and human buccal epithelial cells. The Cy@CD was synthesized using one-step simple microwave-assisted hydrothermal synthesis with precursors, namely, cysteamine and 50X TAE buffer. The spectroscopic characterization of Cy@CD showed (λex/λem) at 350/434 nm with a decent quantum yield of 13.2%. Cy@CD was deployed in tagging bacterial cells such as E. coli, S. aureus, P. aeruginosa and B. subtilis and human buccal epithelial cells. The multicolour emissive Cy@CD tagged microbial cells were also cross-validated by fluorometry analysis. The fluorescent Cy@CD could be used as an ideal substitute for the harmful synthetic fluorescent stain in cell imaging applications.

Electrochemical oxidation of conjugated bilirubin has been studied on an indigenously screen-printed carbon electrode (SPCE). Microscopic, spectroscopic and electrochemical methods thoroughly characterized the electrode. The surface morphology of SPCE revealed graphite nanoparticles of size around 100 nm. The oxidation of bilirubin occurred on SPCE at lower anodic potential and was highly selective towards conjugated bilirubin in the presence of interfering molecules. The SPCE showed a dynamic detection range of 1–600 µM. Conjugated bilirubin spiked urine samples were tested on SPCE and found excellent response.

Magnetic actuation is promising in realizing flow-control devices because of the simplicity in in fabrication and its fast response. A normally-closed active microvalve based on magnetic actuation has been designed, simulated and fabricated for controlled delivery of fluids. By incorporating magnetic particles onto a deflectable membrane, the magnetic activity can be tuned and the actuation can be controlled using an electromagnet. Studies were focused to optimize the design and thickness of the deflectable membrane and the incorporation of magnetic nanoparticles for efficient actuation. Magnetic actuation was carried out using a programmed microcontroller that controls the activity of individual electromagnets which in turn controls the deflection of the membrane. The geometries were designed using CADian and CleWin software and deflection of the membrane was analyzed using computational fluid dynamics (CFD) tool Comsol Multiphysics. The optimized design was fabricated using direct laser write lithography following standard procedures and the simulation results were verified experimentally.

This paper describes the design and fabrication of a microfluidic device for lab on a chip (LOC) applications. Homogenous fluid coverage in the detection well was studied using two and three layer LOC prototypes. Top and middle layer of the device were made of polydimethylsiloxane (PDMS) and bottom layer (LB) with polyethylene terephthalate (PET). The introduction of middle layer increased the depth of detection wells. Inorder to increase the hydrophilicity and hence the uniform well filling, the top layer was treated with PEG. The bonding between layers was performed by corona oxidation and uncured PDMS as adhesive. Carbon electrodes were printed on PET sheet and bonded with middle layer. The performance of LOC device was validated by analyzing the electrochemical response of redox species o-phenylenediamine.

Liver disorders are a widespread health problem and a leading cause of morbidity and mortality in developing countries. The mortality rate due to liver disorders can be reduced significantly by systematic monitoring of proteins that act as liver function biomarkers. This paper demonstrates the design and fabrication of a paper based microfluidic device for the quantification of total protein in blood. The fabrication of microchannels was carried out using wax printing. The total protein concentration in the range of 0 to 14 g dL -1 were successfully measured using the fabricated paper device with the lower limit of detection being 0.5 g dL -1 . The device also showed excellent specificity and repeatability. Total protein in blood serum samples was tested using the device and the obtained results were validated with conventional laboratory methods.

This paper describes the electrochemical exfoliation of graphene from a graphitic electrode in sulphuric acid medium. Parameters such as applied potential, electrolyte concentration and duration of electrolysis were optimized for the synthesis of single layered graphene sheets. Copper oxide –graphene composite was synthesized and used for the fabrication of a disposable nonenzymatic glucose sensor. The electrochemical detection of glucose on the CuO/graphene composite electrode was studied extensively using voltammetric and amperometric techniques

In this work Nickel-Aluminium layered double hydroxide (LDH) was successfully synthesized via urea hydrolysis method. This involves the digestion of aluminium sulphate, nickel sulphate and urea at 90 ⁰C for 24 hours. Atomic force microscopic (AFM) studies revealed the presence of highly ordered layers and the Ni-Al LDH was observed to be in the hexagonal cubic crystalline structure through X-ray diffraction studies. The prepared compound was utilized for fabrication of a non-enzymatic electrochemical glucose sensor. Glucose oxidation on the sensor occurred at 0.6 V in 0.1 M NaOH. The sensor exhibited a sensitivity of4.12 µA/mM/cm2 with linearity upto28 mM. The developed sensor was sensitive towards glucose in the presence of common interfering molecules such asascorbic acid, uric acid, dopamine and creatinine.

The authors describe a disposable non-enzymatic sensor for ascorbic acid (AA) that was obtained by modifying a screen printed electrode (SPE) with Cu(OH)2 nanorods (NRs). The NRs were synthesized by a wet chemical process which involves sequential addition of NH3 and NaOH to CuSO4 solution. NR formation was confirmed by thermogravimetric, spectroscopic, microscopic, and diffraction studies. The Cu(OH)2 NRs were mixed with carbon ink and printed onto an SPE. Electrochemical detection of AA was carried out at pH 7.4, at a typical voltage as low as 0 mV versus saturated calomel electrode with a scan rate of 100 mV/s, and is assumed to involve the chemical reduction of Cu(II) by AA followed by electrochemical oxidation of Cu(I). The sensor has a linear response in the 0.0125 to 10 mΜ AA concentration range. Response to AA is free from interference by urea, glucose, uric acid, dopamine, metal ions such as Fe2+, Zn2+ and Ni2+, NaCl, KCl and ethanol. It was applied to the determination of AA in a vitamin C tablet and in urine.

A disposable non-enzymatic sensor for creatinine was developed by electrodepositing copper on screen printed carbon electrodes. The sensor was characterized using electrochemical and microscopic techniques. Electrochemical detection of creatinine was carried out in phosphate buffer solution of pH 7.4. The estimation was based on the formation of soluble copper-creatinine complex. The formation of copper-creatinine complex was established using the pseudoperoxidase activity of copper-creatinine complex. The sensor showed a detection limit of 0.0746 μM with a linear range of 6–378 μΜ. The sensor exhibited a stable response to creatinine and found to be free from interference from molecules like urea, glucose, ascorbic acid and dopamine. Real sample analysis was carried out with blood serum.

Highly ordered titanium dioxide (TiO₂) nanotubes were modified with CuO mesoclusters through electrodeposition followed by electrooxidation. Field Emission Scanning Electron Microscopy (FESEM) revealed the presence of vertically aligned TiO₂ nanotubes with a diameter of 60 nm and CuO mesoclusters of ~500 nm in diameter. Glucose oxidation on the CuO modified TiO₂ electrode occurred at +0.55 V. The electrode exhibited a sensitivity of 1836 and 1416 μA mmol⁻¹ L cm−2 for glucose concentrations ranging from 0.625 to 6.25 mmol L⁻¹ and 6.87 to 12.5 mmol L⁻¹ respectively, a limit of detection of 3.4 μmol L⁻¹ (S/N = 3) and a rapid response time of ≤2 s. Physiological concentrations of ascorbic acid, uric acid and dopamine had no effect on the glucose oxidation. Interference from other sugars (lactose and galactose) was negligible. Result obtained from the estimation of blood glucose was found to be in good agreement with those obtained from commercially available glucose sensor strips.

A disposable nonenzymatic glucose sensor was obtained by pulsed electrodeposition of Pt-CuO on a graphite pencil electrode (GPE). The morphology of the modified GPE was studied using SEM, and the chemical composition of the coating was examined by EDAX and XRD. The electrochemical response of the modified GPE was compared with individual copper- and platinum-modified GPEs. The electrodeposition parameters were optimized with respect to the electrocatalytic activity of the deposits towards glucose oxidation. Best operated at a working potential of 0.6 V vs. Ag/AgCl, the sensor has a sensitivity of 2035 μA mM−1 cm−2, a 0.1 μM detection limit and a wide linear response range that extends up to 25 mM. It is highly selective for glucose in the presence of various exogenous and endogenous interfering species. Eventhough the requirement of alkaline medium for sensing is a limitation, easy fabrication procedure, very high sensitivity and selectivity, wide analytical range, and disposable sensor characteristics show potential application towards blood glucose determination.

Carbon dots co-doped with nitrogen and sulfur (NSCDs) were obtained from thiourea and TAE (Tris-acetate-ethylenediamine) buffer using microwave assisted hydrothermal synthesis. The synergistic presence of nitrogen and sulfur as a dopant results in teasing fluorescence properties and a fluorescence quantum yield of 57%. An HR-TEM study showed the NSCDs to be mono-dispersed and seemingly spherical with an average hydrodynamic diameter of 3.6 ± 0.88 nm. The NSCDs are nontoxic as proven by an MTT assay for cytotoxicity. The optical characterization was done by using UV-Vis absorption and fluorescence spectroscopy which revealed excitation wavelength-dependent multicolor emissions. The characterization of surface topology was done by using X-ray diffraction, FTIR, and X-ray photoelectron spectroscopy. The NSCDs were used to image various pathogenic bacteria (E. coli, Klebsiella, PseudomonasStaphylococcus) and human buccal epithelial cells by applying multicolor fluorometry. Graphical abstract Schematic presentation of microwave-assisted hydrothermal synthesis of nitrogen and sulfur doped carbon dots (NSCD) based on Thiourea and 50X Tris-acetate-ethylenediamine (TAE) buffer having multicolor fluorescence, used for tagging and imaging pathogenic bacteria and Human buccal epithelial cells using fluorescence microscope.

Electrochemical detection of cholesterol has been carried out on pencil lead electrode (PLE) in acetonitrile and acetone (1:1 v/v %) containing 0.3 M lithium perchlorate. The PLEs were explored for the first time for the detection of cholesterol in an organic medium. The electrodes were thoroughly characterized by microscopy and diffraction studies. The PLE exhibited a wide linear range of detection from 0.625 to 9.375 mM and high sensitivity of 1455.22 μA mM−1 cm−2. These characteristics point to the superior performance of the sensor when compared with that reported in the organic medium. The unmodified PLE was highly specific to cholesterol in the presence of commonly interfering biomolecules such as uric acid, dopamine, glucose, ascorbic acid, creatinine and proteins. Calibration plots for real samples were constructed by spiking 0.625–9.375 mM of cholesterol to serum and skin cholesterol samples. In both samples, the PLE show a highly linear response.

We present an analysis of the effect of incorporating ridges in straight and meander shaped pressure-driven Y-type micromixers. Triangular and rectangular ridges were incorporated on the inner walls of straight and meandered microfluidic channels, and their effect on mixing was evaluated. The incorporation of ridges greatly enhances mixing in the flow path due to strong laminar perturbations. Also, the effect of the geometry of ridges and their arrangement pattern in the microchannel was studied extensively. Incorporation of ridges in the microchannels resulted in enhanced performance of the mixer in terms of reduction in mixing time and length. Meander channels with ridges provided greater than 90 % mixing in less than 2 mm, whereas straight channels with ridges required a mixing length of 10 mm. The optimum design was fabricated using direct-laser write photolithography followed by soft lithography. The performance of the micromixer was validated using coloured solutions and biosensors. The micromixer is compact, simple in fabrication and operation, and easy-to-integrate with other microfluidic components enabling them for real-time applications. Its scope for the development of microfluidic devices where mixing is crucial has been demonstrated using glucose biosensors.

An elemental, non-metallic red phosphorus-based photocatalyst for potential continuous flow disinfection of water is reported. The crystalline red phosphorus is immobilized by a solid state method on the inner walls of a quartz capillary tube and a continuous flow photocatalytic disinfection of E. coli solution under direct sunlight is demonstrated using the set-up as an optofluidic reactor. Structural and microstructural analyses employing electron diffraction confirms the fibrous phase of the immobilized red phosphorus. The reactor with the immobilized photocatalyst when tested under direct sunlight resulted in a 6.7 log reduction (>99.9999% reduction) in the concentration of E. coli bacteria within 14 min. The sample aliquot collected at 28 min residence time did not yield any visible colonies indicating the high efficiency of the process. The demonstrated efficiency suggests great potential for commercial scale-up.

A simple approach is followed for the fabrication of disposable nonenzymatic hydrogen peroxide (H 2 O 2 ) sensor using gold nanoparticles decorated reduced graphene oxide (Au/rGO) nanocomposite. Au/rGO nanocomposite was prepared by one pot reduction of graphene oxide and Au(III) ions. The composite was characterized using various spectroscopic and microscopic techniques. The Au/rGO nanocomposite suspension was cast on the indigenously fabricated screen printed electrode (SPE). Voltammetric studies on the modified electrode showed that the Au/rGO nanocomposite modified SPE have enhanced catalytic activity towards H 2 O 2 . The sensor exhibited linear relationship in the range from 20 μM to 10 mM with a sensitivity of 1238 μA mM − 1 cm − 2 and a limit of detection 0.1 μM. The sensor also showed excellent selectivity in presence of other electroactive species such as ascorbic acid, dopamine, glucose and uric acid.

Hexavalent chromium is an important inorganic industrial effluent in the water that causes serious health problems to the mankind. Photocatalytic reduction of Cr(VI) is a green technology that converts the toxic Cr(VI) to non-toxic Cr(III). In the photocatalytic reduction of Cr(VI), transition metal oxide semiconductors are mainly used as photocatalysts. This infers, for the removal of a transition metal i.e. Cr(VI), another transition metal is added in the form of photocatalyst. Hence, we explore a non-metallic, elemental photocatalyst fibrous red phosphorus (FRP), a crystalline allotrope of red phosphorus as photocatalyst for Cr(VI) reduction. FRP exhibits excellent photocatalytic activity towards Cr(VI) reduction under direct sunlight and we observed complete reduction of Cr(VI) (25 mg/L) within 40 min at pH-2.

Rapid detection of lethal pathogens is critical to abate the mortality rate of patients suffering from infectious diseases. Herein, we report a pH-sensitive detection of the pathogenic bacteria using multicolor emissive Nitrogen-doped Carbon Dots (NtCD) synthesized by a one-step hydrothermal method. The unique pH-sensitive interaction of NtCD with bacteria was best studied at pH 2. NtCD was competent to detect several pathogenic bacteria such as; Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), Bacillus subtilis (B. subtilis) and Proteus vulgaris (P. vulgaris). The fluorescence spectral investigations of NtCD revealed the excitation dependent emission property with a red-shift. It shows an intense photoluminescent (PL) emission at λex/λem = 340/435 nm. The calculated quantum yield of NtCD was 27.2%. It also possesses multicolor emission at different excitation wavelengths. TEM analysis displayed the uniform spherical morphology of NtCD particles with an average hydrodynamic diameter of 3.11 ± 0.75 nm. The zeta potential of NtCD was measured as −8.4 mV at pH 2. The interaction between NtCD and bacteria was explained on the basis of their zeta potential values. The PL emission response of NtCD tagged bacteria was investigated at λex = 340 nm. It was potentially tagging to both E. coli and S. aureus but with a better response towards E. coli cells. The human squamous epithelial cells (SEC) were deployed as a fitting substitute for achieving NtCD-mammalian cell imaging. Both NtCD tagged bacterial cells and SEC exhibited multicolor emission as well. Mechanistic implications of pH-dependent PL emission property of NtCD and its bacterial interaction were discussed extensively.

Low cost SERS substrates are imperative to develop single use, point of care diagnostics. In the quest for such SERS substrates, we developed a wet chemical method to produce Cu nanowire like networks. The oriented attachment and coalescence observed in these network like nanostructures infer their aggregation behavior that ultimately results in the generation of exciting inter-particle junctions. The hot spots formed by these inter-particle junctions certainly increases the electromagnetic enhancement. SERS activity of these substrates is evaluated using methylene blue (MB) molecule and found activity enhancement by a factor of 1.1 × 104.

A nonenzymatic glucose sensor was fabricated by electrodepositing cobalt rich cobalt–copper alloy nanoparticles (Co–CuNPs) on vertically aligned TiO2 nanotube (TDNT) arrays. For this, TDNT arrays with tube diameter of 60 nm were synthesized by electrochemical anodization. The composition of the electrodeposited alloy was optimized based on the electrocatalytic activity towards glucose oxidation. This is achieved by controlling the concentration of electrolyte and time of deposition. Chemical composition of the optimized Co–Cu alloy nanoparticles is determined to be Cu0.15Co2.84O4 with fcc crystalline structure. The sensor showed two linear range of detection with high sensitivity of 4651.0 μA mM−1 cm−2 up to 5 mM and 2581.70 μA mM−1 cm−2 from 5 mM to 12 mM with a lower detection limit of 0.6 μM (S/N = 3). The sensor is highly selective to glucose in the presence of various exogeneous and endogeneous interfering species and other sugars. The response of the sensor towards blood serum was in good agreement with that of commercially available glucose sensors.

A nonenzymatic electrochemical glucose sensor was fabricated using gold–copper oxide nanoparticles decorated reduced graphene oxide (Au–CuO/rGO). A novel one step chemical process was employed for the synthesis of nanocomposite. Morphology and crystal planes of the nanocomposite were characterized using high resolution scanning electron microscopy (HRSEM) and X-ray diffraction (XRD) respectively. The Au–CuO/rGO nanocomposite was dispersed in N,N-dimethyl formamide (DMF) and drop-casted on the working area of the indigenously fabricated screen printed electrode (SPE). The sensor showed good electrocatalytic activity in alkaline medium for the direct electrooxidation of glucose with linear detection range of 1 μM to 12 mM and a lower detection limit of 0.1 μM. The sensor exhibited an excellent sensitivity 2356 μA mM−1 cm−2. Sensor was used for the determination of serum glucose concentration and the results obtained were compared with commercially available test strips.

An electrochemical immunosensing platform based on dual signal amplification strategy has been developed using gold nanoparticles. Human Immunoglobulin G was used as a model analyte in order to establish the immunosensing platform. The platform was fabricated using of 1,6-hexanedithiol self assembled on a gold disc electrode and was further modified by citrate capped gold nanoparticles. The direct immobilization of antibody was achieved through electrostatic interaction between negatively charged citrate capped gold nanoparticles and positively charged amino group of antibody. Each step of modification was analyzed using electroanalytical techniques like cyclic voltammetry and electrochemical impedance spectroscopy. The horseradish peroxidase (HRP)-labeled secondary antibodies conjugated on gold nanoparticles (AuNP-Ab2) acted as nanolabels. Thus the sandwich immunocomplex formed on the electrode surface produced an electrocatalytic response through the reduction of hydrogen peroxide by HRP in the presence of thionine. Electrochemical studies were carried out to understand the role of citrate capped AuNP and AuNP-Ab2 in dual signal amplification. The fabricated sensing platform can be used for the sensitive determination of various protein biomarkers by immobilizing specific antibody.

Graphene oxide (GO) with photoluminescent property was prepared by modifiedHummer’s method. Spectroscopic and morphological studies were carried out using photoluminescence spectroscopy, UV-Vis absorption spectroscopy, FT-IR, XRD and FE-SEM. Electrochemical dopamine sensor was fabricated by drop casting GO onto screen printed carbon electrodes (SPCE). Cyclic voltammogram, differential pulse voltammogram and amperometry were performed to test the fabricated sensor. The sensor exhibits wide detection range of 12.5 μM to 1 mM dopamine concentrations in 0.1 M PBS of pH 7.4. The major interferents such as ascorbic acid shown negligible current response compared to dopamine.

Uniform and rapid mixing between various streams in a microfluidic device is essential for the development of device involving reaction between multiple streams. In this work, microfluidic channels of various geometries were designed and their fluid flow patterns were analyzed to optimize complete mixing of different fluids. The designs were modified by incorporating different types of ridges (square, curved and triangular shaped) in the microfluidic channels. Numerical analysis of the designs was carried out using COMSOL Multiphysics 4.3a. The extent of mixing in each of the design was calculated and the optimized design was fabricated using photolithography followed by soft lithography. The performance of the developed micromixer was studied using colored solutions and it was found to be in good agreement with the simulated results.

Rapid and reliable method for the selective detection of pathogenic bacteria is critical in environmental monitoring, disease control, food safety and for the diagnosis of infectious diseases. In this study, we have synthesized hydrophilic fluorescent CdSe Quantum dots (CDSe QDs) and characterized using UV-Vis, IR and fluorescence spectroscopy. Crystallinity of the synthesized Qdots were analysed using XRD. As synthesized CdSe QDs were used for the imaging of buccal epithelial cells and pathogenic bacteria. Selectivity of CdSe QDs to detect E. coli was improved by the functionalization of QDs with glycerol. Easy imaging steps and decreased imaging time with the current procedure shows the potential for biomedical imaging.

Fibrous red phosphorus (FRP), a crystalline allotrope of red phosphorus has interesting structural features and promising applications in the area of energy storage devices and photocatalysis. In this work, we employ a solid state method to synthesize crystalline red phosphorus which results in an interesting urchin-like structure. The microstructure shows a bundle of fibers originating from a core. Detailed characterization points to the presence of FRP as the major allotrope in the product. Photocatalytic activity of FRP is examined towards the solar disinfection of water using E. coli as a model pollutant. The bandgap of the synthesized FRP is 1.9 eV and it has optimum valence band and conduction band levels to generate reactive oxygen species (ROS) such as superoxide radical and H2O2. OH· is then produced from the H2O2. These photo-generated ROS are successful in bringing 8 log reduction in the concentration of E. coli in 30 min, which compares extremely well with values reported from other catalysts.

Computational simulation for the fluid flow in a paper based microfluidic system was performed and was experimentally validated in this work. Comsol Multiphysics based simulation was performed and the module used was species transport in porous medium. Two separate simulation for the reagent distribution and the interaction of sample with the immobilized reagent in paper based microfluidics devices were carried out. This was performed by varying the parameters such as adsorption constant, diffusivity and average velocity of fluid in the porous medium for finding the concentration profile. Finer mesh were used for the simulation which gives more accurate results with less computational time. The reagent distribution was experimentally validated by dropping methylorange indicator over Whatman filter paper.

Cu nanowires are important class of one dimensional metal nanowires with high electrical conductivity comparable to silver nanowires. Sophorolipid (SL), a well-known biosurfactant and glycolipid, plays significant role in the synthesis of nanomaterials as reducing and capping agent. Herein, we report the synthesis of Cu nanowires using sophorolipid by alkyl amine mediated hydrothermal synthesis and in this process, octadecylamine (ODA) used as alkyl amine. Cu nanowires of length ∼ 5 − 40 μ m and width ∼ 50 − 250 nm are produced at SL/ODA weight ratio of 0.13:1. Further structural investigations suggest that the morphology of these Cu nanostructures changes from nanowires to micron size rods and decahedron particles by modulating the weight ratio of SL and ODA.