Sheela Berchmans

Self-assembled monolayers of 2-mercaptobenzimidazole on gold: stripping voltammetric determination of Hg(II)

Monomolecular level modification of electrode surfaces through a self-assembly approach is, of late, gaining importance in view of its many functional applications in areas such as molecular electronics, molecular recognition, electron transfer studies and electroanalysis. Self-assembled monolayer (SAM) modification of a gold electrode with 2-mercaptobenzimidazole (MBI) has been achieved. On this modified electrode, anodic stripping voltammetric determination of mercury at ppm/sub-ppm level concentrations has been successfully attempted. Pre-concentration, prior to stripping, has been effected through a non-electrolytic process involving chemical interactions between MBI and Hg(II). The results are described and discussed with a plausible scheme.

Bioelectrocatalysis of Acetobacter aceti and Gluconobacter roseus for current generation.

Acetobacter aceti and Gluconobacter roseus, which are known to be responsible for the spoilage of wine, are used for current generation in batch-type microbial biofuel cells and it has been shown for the first time that these two microorganisms do not require mediators for the transfer of electrons to the anode. Three biofuel cells were constructed with two cells containing the pure cultures of each of the microorganisms as the biocatalyst (A-MFC, G-MFC) and the third cell was constructed with the mixed culture of these two microorganisms as the biocatalyst (AG-MFC). The performance of the biofuel cells was evaluated in terms of open circuit voltage (OCV), fuel consumption rate, internal resistance, power output, and coulombic efficiency. The mixed culture cell (AG-MFC) exhibits a better overall performance compared to the other cells.

Facile and green synthesis of graphene

Herein, we report a simple, facile, green and cost effective strategy for the synthesis of graphene using naturally available anti-oxidants such as carotenoids present in vegetable (carrot, sweet potato, etc.) extracts. In this work, we have employed carrot extract to reduce graphene oxide to reduced graphene oxide. A red shift (in the λmax from 230 nm to 270 nm) during the course of the reduction of GO clearly indicates the effective restoration of the sp2 graphitic carbons. In addition, we have also noticed the colour change of the reaction mixture from yellowish brown to black after 1 hour, thereby indicating the reduction of GO to reduced graphene oxide (Ct-RGO). Further, an increase in the D/G ratio value of GO from 0.979 to 1.198 after the complete reduction indicated the effective restoration of the in plane sp2 domains in the Ct-RGO. The morphology and conductivities of the Ct-RGO are characterized by several characterization techniques such as UV, FT-IR, Raman, XRD, XPS, SEM, TEM, AFM and EIS. The green synthesis reported in this work is expected to yield a biocompatible graphene material suitable for futuristic biological applications.

Non-enzymatic detection of bilirubin based on a graphene–polystyrene sulfonate composite

We report, a selective, non-enzymatic bilirubin (BR) detection through catalytic oxidation on a reduced graphene oxide (RGO)–poly styrene sulfonate (PSS) composite film spin coated on a glassy carbon electrode. The catalytic ability, stability, morphology and composition of the RGO–PSS composite, were evaluated using voltammetric, spectroscopic and microscopic techniques. The experimental variables influencing the analysis of bilirubin were optimized in terms of active material composition, pH and serum albumin concentration in blood. At the optimized condition, the linear dynamic range was found to be 0–450 μM, with a sensitivity of 0.16 μA μM−1 cm−2 and the detection limit was 2.0 μM. The modified electrode possesses good stability, reproducibility and selectivity towards bilirubin determination. The real sample analysis demonstrates the scope of the RGO–PSS composite modified electrode for practical clinical diagnosis.

The three-compartment microbial fuel cell: a new sustainable approach to bioelectricity generation from lignocellulosic biomass

Herein, we report a new strategy for the simultaneous degradation of lignocellulosic biomass and bioelectricity generation using a novel three-chamber microbial fuel cell (MFC). Oscillatoria annae, a freshwater cyanobacterium, was used for the hydrolysis of cellulose to glucose. The electrocatalytic activity of the coculture of Acetobacter aceti and Gluconobacter roseus was used to oxidize the glucose for current generation in the MFC. Carbon felt was used as the anode and cathode material. Lignocellulosic materials such as sugarcane bagasse and corn cob were used as substrates. The performances of the MFC with two different substrates were analyzed by polarization studies, coulombic efficiency, percentage of COD removal and internal resistance. The three-chamber MFC produced a maximum power output of 8.78xa0W/m3 at 20.95 A/m3 and 6.73xa0W/m3 at 17.28 A/m3 with sugarcane bagasse and corn cob as substrates, respectively.Graphical Abstract

Electrochemical amination of graphene using nanosized PAMAM dendrimers for sensing applications

In this work, a graphene film was electrochemically functionalized by anodic oxidation of amine terminated PAMAM (4th generation PAMAM-(NH2)64) dendrimer molecules via a covalent linkage (C–N) between graphene and PAMAM. This simple functionalization provides ≈37.51 × 1015 PAMAM molecules per cm2 on the versatile graphene, which is eleven times higher than the PAMAM molecules attached on the glassy carbon electrode (3.33 × 1015 molecules per cm2). Thus, the facile electrochemical functionalization route on graphene yields a high density of amine functional groups on graphene which offers an opportunity to load a larger number of enzymes, proteins, DNA, antibodies, antigens, etc. to develop highly sensitive graphene based bio and chemical sensors. To demonstrate this with a model, the horseradish peroxidase enzyme was immobilized onto the functionalized graphene film to detect H2O2. The as constructed platform shows enhanced electrocatalytic activity, high storage stability up to one month, lower applied potential and exhibits a high sensitivity of 29.86 μA mM−1 cm−2 which was 5 times greater than the functionalized GCE for the detection of H2O2. The sensor was also used to detect H2O2 in human serum to testify the feasibility of the sensor in practical application. These results demonstrate that the electrografting of PAMAM on graphene is a promising approach for the fabrication of the sensors which exhibit enhanced electrocatalytic activity, sensitivity and stability.

Synergistic effect of hydroxypropyl-β-cyclodextrin encapsulated soluble ferrocene and the gold nanocomposite modified glassy carbon electrode for the estimation of NO in biological systems

An electrochemical assay for sensing NO in biological systems is described in this paper. The ferrocene mediated reduction of NO, facilitated by the gold nanocomposite modified glassy carbon electrode is followed by an amperometric procedure. The analytical protocol involves the modification of a glassy carbon electrode by an overlayer of Au nanocomposites prepared through galvanic reduction. Additional overlayers can be built on the surface by repetition of the procedure. The modification leads to the decrease of the over-potential required for the analysis and results in a non-biofouling surface. Since the procedure is based on the electrochemical reduction of NO, the potential interferences from species like dopamine, ascorbic acid, etc., are overcome. The sensitivity, detection limit and response time achieved through this protocol for the modified electrode containing three Au overlayers are 0.03 nA/nM, 25.75 nM and <5 s. Analysis of NO has been carried out in real samples like liver extract, peripheral blood mononuclear cells (PBMCs) and miconazole nitrate ointment and the values obtained are comparable with that obtained by Griess analysis.

Symbiosis of photosynthetic microorganisms with non-photosynthetic ones for the conversion of cellulosic mass into electrical energy and pigments

In this article, we report a three-compartment microbial fuel cell (MFC) system for the simultaneous degradation of cellulose and production of natural pigments such as phycoerythrin and phycocyanin along with bioelectricity generation. Oscillatoria annae, a freshwater cyanobacterium, was used for the conversion of cellulose to reducing sugars, which were fed as a substrate to a coculture of Acetobacter aceti and Gluconobacter roseus for current generation in a three-compartment MFC. Carbon felt modified with a composite film containing chitosan and sodium alginate served as the MFC anode. The cellulose-fed three-compartment MFC produced a maximum power output of 6.62xa0Wxa0m−3 at 17.55xa0Axa0m−3.Graphical AbstractThis work couples the catalytic activity of O. annae, a freshwater cyanobacteria, and electrogenic activity of Acetobacter aceti and Gluconobacter roseus for electricity generation and pigment production.

Naked eye detection of nitric oxide release from nitrosothiols aided by gold nanoparticles

In this work we have demonstrated that nitric oxide can be monitored spectrophotometrically using cyclodextrin encapsulated ferrocene. The detection course showed the colour change from yellow to blue which can be detected with the naked eye. Also we describe the catalytic effect of gold nanoparticles in enhancing nitric oxide release from S-nitrosothiols.

Tailored interfacial architecture of chitosan modified glassy carbon electrodes facilitating selective, nanomolar detection of dopamine

Herein, it is demonstrated that the sulfonation of chitosan (CS) on a glassy carbon surface (GCE) facilitates the making of a new sensing platform for the selective, nanomolar detection of dopamine. The surface functionalisation of CS was carried out using sulphamic acid (SA) by simple glutaraldehyde (GA) cross-linking to yield the sulfonated derivative (GCE–CS–GA–SA). The sulfonated chitosan possesses sulfonic acid functionalities which provide an electrostatic barrier, thereby discriminating dopamine from ascorbic acid. Electrochemical techniques, branded for their accuracy and fast response, are employed to determine dopamine concentrations down to few nanomoles in the presence of high concentrations of AA. In addition to nanomolar detection, the reported sensing methodology exhibits a low dopamine oxidation potential of 210 mV vs. normal calomel electrode (NCE) and wide linear ranges of 50 nM to 10 μM and 10–400 μM in chronoamperometry and differential pulse voltammetry, respectively. These results reveal that an inexpensive, simple and facile functionalization of chitosan like polymers on carbon surfaces can open up new avenues in the creation of perm-selective membranes that can find application in novel biosensors fabrication, especially in electrophysiology.