Sivaprakasam Radhakrishnan

Facile fabrication of NiS and a reduced graphene oxide hybrid film for nonenzymatic detection of glucose

In the present study, nickel sulfide (NiS) decorated reduced graphene oxide was synthesized by a facile one-step hydrothermal approach. Characterization of the as-made nanohybrid using a Field emission scanning electron microscope (FE-SEM) and powder X-ray diffraction (XRD) clearly demonstrate the successful attachment of NiS onto the rGO nanosheets. Further, the prepared NiS–rGO nanohybrid has been examined for the electrochemical nonenzymatic detection of glucose using cyclic voltammetry, linear sweep voltammetry and amperometry. The electrochemical studies demonstrated that the NiS–rGO nanohybrid modified electrode detects glucose linearly over a concentration range of 5.0 × 10−5 to 1.7 × 10−3 M with a detection limit of 1.0 × 10−5 M. The obtained detection limit for the NiS–rGO nanohybrid is very much comparable to the recent literature values. Further, the NiS–rGO nanohybrid modified electrode showed an excellent anti-interference ability against electroactive species and showed good reproducibility and stability.

An enzymatic biosensor for hydrogen peroxide based on one-pot preparation of CeO2-reduced graphene oxide nanocomposite

The study describes cerium oxide-reduced graphene oxide (CeO2-rGO) prepared by a facile one-pot hydrothermal approach and its assembly with horseradish peroxidase (HRP) for the detection of hydrogen peroxide (H2O2) at trace levels. The prepared nanocomposite was characterized by Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, X-ray diffraction, and voltammetry. Furthermore, the direct electrochemistry of HRP/CeO2-rGO composite has been studied. The immobilized enzyme retained its bioactivity and exhibited a pair of well-defined redox peaks, confirming the direct electron transfer (DET) of HRP with CeO2-rGO composite modified electrode. A significant enzyme loading (4.270 × 10−10 mol cm−2) has been obtained on CeO2-rGO composite as compared to the bare glassy carbon (GC), CeO2, and rGO modified surfaces. This HRP/CeO2-rGO film has been used for the sensitive detection of hydrogen peroxide by voltammetry and it exhibited a wide linear range of H2O2 from 0.1 to 500 μM with a detection limit of 0.021 μM. The apparent Michaelis–Menten constant (KappM) of HRP on the CeO2-rGO composite was estimated as 0.011 mM. The combination of the direct electron transfer character of HRP and the promising feature of CeO2-rGO composite favors the sensitive determination of H2O2 with improved sensitivity.

Riboflavin detection by α-Fe2O3/MWCNT/AuNPs-based composite and a study of the interaction of riboflavin with DNA

The electrochemical behavior of riboflavin (RF) at a glassy carbon electrode modified with α-Fe2O3/MWCNT/AuNPs was investigated by cyclic voltammetry (CV) and square wave voltammetry (SWV). The redox behavior of the RF was examined in detail in phosphate buffer solution using variable scan rate cyclic voltammetry (V = 20 mV s−1–10 V s−1) and has been found to undergo a series of proton-coupled electron transfer reactions. Moreover, the interaction of RF with double stranded DNA (ds-DNA) based on the oxidation signal of the guanine base was studied using SWV. Our sensor fabrication did not take into account the pretreatment procedure of the modified electrode to immobilize the ds-DNA, which shows that our composite material has highly electroactive and many functional groups to interact with ds-DNA. The decrease in the intensity of the guanine oxidation signal after interaction with RF was found as an indicator signal for the sensitive determination of RF. These results additionally confirmed that this RF–ds-DNA interaction could be used for sensitive and accurate detection of RF. The peak current on the modified electrode was linear over a range from 0.3 μM to 0.6 × 10−8 M, with the detection limit of 6 nM (3σ/b). The analytical performance of this sensor was demonstrated in real samples with satisfactory recovery.

A new strategy for simultaneous determination of 4-aminophenol, uric acid and nitrite based on a graphene/hydroxyapatite composite modified glassy carbon electrode

A novel electrochemical sensor has been fabricated based on a graphene/hydroxyapatite nanocomposite modified glassy carbon electrode (GCE) for the selective and simultaneous detection of 4-aminophenol (4-AP), uric acid (UA) and nitrite ions (NO2−) in a phosphate buffer solution (PBS, pH 7.0) for the first time. The modified electrode exhibited improved electrocatalytic activity towards the oxidation of 4-AP, UA and NO2− in the form of three strong peaks in both the cyclic voltammetry (CV) and square wave voltammetry (SWV) techniques. Under optimum conditions, the ternary system comprising 4-AP, UA and NO2− exhibited linear calibration plots over a wide range of 0.1–425 μM, 1–1000 μM and 3–950 μM with detection limits of 0.29 μM, 0.03 μM and 0.025 μM for 4-AP, UA and NO2− respectively. The developed sensor displayed high sensitivity and low detection limits coupled with good stability and reproducibility which were attributed to the synergistic effect of graphene and HAP in the nanocomposite. In addition, the fabricated sensor was applied to the determination of UA, 4-AP and NO2− in urine and tap water samples with satisfactory results.