Chiranjeevi Srinivasa Rao Vusa

Selective and efficient electrochemical biosensing of ultrathin molybdenum disulfide sheets

Atomically thin molybdenum disulfide (MoS₂) sheets were synthesized and isolated via solvent-assisted chemical exfoliation. The charge-dependent electrochemical activities of these MoS₂ sheets were studied using positively charged hexamine ruthenium (III) chloride and negatively charged ferricyanide/ferrocyanide redox probes. Ultrathin MoS₂ sheet-based electrodes were employed for the electrochemical detection of an important neurotransmitter, namely dopamine (DA), in the presence of ascorbic acid (AA). MoS₂ electrodes were identified as being capable of distinguishing the coexistence of the DA and the AA with an excellent stability. Moreover, the enzymatic detection of the glucose was studied by immobilizing glucose oxidase on the MoS₂. This study opens enzymatic and non-enzymatic electrochemical biosensing applications of atomic MoS₂ sheets, which will supplement their established electronic applications.

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.

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.

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.

Tactical tuning of the surface and interfacial properties of graphene: A Versatile and rational electrochemical approach

Designing a versatile and rational method for the tactical tuning of the surface and interfacial properties of graphene is an essential yet challenging task of many scientific areas including health care, sensors, energy, and the environment. A method was designed herein to tackle the challenge and tune the surface and interfacial properties of graphene using a simple electrochemical tethering of arylamines that provides diverse reactive end groups to graphene. This method resulted in the preparation of graphenes with thiol, hydroxy, amine, carboxyl, and sulfonate surface functionalities respectively. X-ray photoelectron spectroscopy, scanning electron microscopy, and cyclic voltammetry were used to study the chemical, morphological, and electrochemical properties of the modified graphenes. The results show the promising scope of the reported method towards the tactical tuning of the surface and interfacial properties of graphene. Also, this method can give fundamental insights of the surface tuning of graphene and its structurally similar materials. Hence, this approach can be used to advantageously tune the surface properties of the other structurally similar nanocarbons and their hybrid materials to make them potential candidates for many applications.