Krishnapillai Girish Kumar

Thioglycolic acid capped CdS quantum dots as a fluorescent probe for the nanomolar determination of dopamine

Thioglycolic acid (TGA) capped CdS quantum dots (QDs) have been successfully employed as an efficient nano sized fluorescent probe for the selective determination of dopamine (DA) in acetate buffer solution (pH 7). The fluorescence emission spectrum of TGA functionalized CdS QDs which was at about 527 nm showed an enormous increase in emission intensity in the presence of DA. The linear range and detection limit of the developed turn on sensor were 3.94 × 10−7 to 4.67 × 10−8 M and 2.55 × 10−9 M, respectively. The addition of DA increases the passivation of surface traps of QDs thereby increasing the fluorescence emission intensity. The influence of some biologically important species that are structurally similar to DA on the fluorescence emission intensity of the CdS fluorescent probe was studied to evaluate the selectivity of the sensor. The developed turn on sensor exhibits good analytical figures of merit and excellent selectivity and shows promising practical applications.

Voltammetric study of pyridine-2-aldoxime methochloride at poly(p-toluene sulfonic acid) modified glassy carbon sensor and its analytical applications

A poly(p-toluene sulfonic acid) (p-TSA) modified glassy carbon electrode (GCE) was fabricated by electropolymerisation using cyclic voltammetry (CV). This chemically modified electrode showed high stability, good selectivity and reproducibility for the determination of pyridine-2-aldoxime methochloride (PAM chloride) a cholinesterase reactivator, used in military as an antidote in the treatment of organophosphate poisoning and to counteract the effects of overdosage by anticholinesterases used in treating myasthenia gravis. Compared with bare GCE, the modified electrode showed an enhancement in the oxidation peak current as well as a reduction in the oxidation potential of PAM chloride. Favorable electrostatic interaction between the negatively charged poly(p-TSA) film and the positively charged drug as well as the formation of hydrogen bonds could contribute to this enhanced sensitivity. Under optimum conditions the oxidation peak current is proportional to the concentration of PAM chloride in the range 1 × 10−3 M to 1 × 10−7 M with a detection limit of 3 × 10−8 M. The developed sensor was also successfully applied for the determination of PAM chloride in body fluids.

Quantum Dots (QDs) Based Fluorescent Sensor for the Selective Determination of Nimesulide

Fluorescent PET (Photoinduced Electron Transfer) has been of particular growth in recent times. A novel PET based fluorescent sensor using unmodified CdSe quantum dots (QDs) has been developed for the trace determination of Nimesulide (NIM). The sensor is based on the selective fluorescence quenching of quantum dots by NIM in presence of other NSAIDs and is found that intensity of quenching is linearly related to NIM concentration in the range 8.2 × 10−7 – 4.01 × 10−5 M. The mechanism of interaction is discussed. Finally, the potential application of the proposed method for the trace determination of NIM in pharmaceutical formulation is demonstrated.

Electroanalysis of trimethoprim on metalloporphyrin incorporated glassy carbon electrode

Trimethoprim (TMP) is a bacteriostatic antibiotic mainly used in the prophylaxis and treatment of urinary tract infections. It belongs to the class of chemotherapeutic agents known as dihydrofolate reductase inhibitors. Its use is associated with idiosyncratic reactions, including liver toxicity and agranulocytosis. In order to determine TMP electrochemically, a metalloporphyrin modified glassy carbon electrode was prepared by coating [5,10,15,20- tetrakis(4-methoxyphenyl) porphyrinato]Mn (III)chloride (TMOPPMn(III)Cl) solution on the surface of the electrode. The electrochemical behaviour of TMP in Phosphate buffer solution (PBS) on TMOPPMn(III)Cl modified glassy carbon electrode (TMOPPMn(III)Cl/GCE) was explored using differential pulse voltammetry (DPV). The voltammograms showed enhanced oxidation response at the TMOPPMn (III)Cl/GCE with respect to the bare GCE for TMP, attributable to the electrocatalytic activity of TMOPPMn(III)Cl. Electrochemical parameters of the oxidation of TMP on the modified electrode were analyzed. The electro-oxidation of TMP was found to be irreversible, pH dependent and adsorption controlled on the modified electrode. It is found that the oxidation peak current is proportional to the concentration of TMP over the range 6 × 10⁻⁸ - 1 × 10⁻⁶ M with a very low detection limit of 3 × 10⁻⁹ M at 2 min open circuit accumulation. The repeatability expressed as relative standard deviation (RSD) for n = 9 was 3.2% and the operational stability was found to be 20 days. Another striking feature is that equimolar concentration of sulfamethoxazole did not interfere in the determination of TMP. Applicability to assay the drug in urine and tablet samples has also been studied.

A silicon nanoparticle based turn off fluorescent sensor for sudan I

Sudan dyes are synthetic colorants which were extensively used in food products before being banned due to their carcinogenic effect on living systems. To regulate their use and to ensure food quality, simple and cost effective methods need to be developed for their determination. A turn off fluorescence sensor based on hexadecylamine capped silicon nanoparticles (Si NPs) has been developed for the quantification of sudan I. The fluorescence of Si NPs was effectively quenched by sudan I via an inner filter effect (IFE). Under optimum conditions, this method can be used for the quantification of sudan I within the concentration range of 2.91 × 10−5 to 4.97 × 10−7 M with a detection limit of 3.90 × 10−8 M. The developed sensor was successfully applied for the determination of sudan I in chilli powder samples.

A colorimetric and fluorometric sensor for the determination of norepinephrine

A colorimetric and fluorometric dual channel sensor has been developed for the determination of norepinephrine (NE). Visual detection is possible due to the formation of brown silver nanoparticles (NPs) in the presence of NE, which further results in strong metal enhanced fluorescence signals. A linear relationship was obtained between the absorbance values and concentration of NE in the range 1.00 × 10−6 M to 6.66 × 10−8 M; the detection limit being 1.79 × 10−8 M. It was also found that the fluorescence intensities were proportional to the concentration of NE over the range of 8.92 × 10−3 M to 5.66 × 10−5 M, with the corresponding limit of detection 5.59 × 10−6 M. Furthermore, application of the present approach in synthetic blood serum has been demonstrated, which suggests its great potential for diagnostic purposes.

A voltammetric sensor for acetaminophen based on electropolymerized-molecularly imprinted poly( o -aminophenol) modified gold electrode

A simple and reliable molecularly imprinted polymer (MIP) based voltammetric sensor has been proposed for the determination of acetaminophen (AP). Gold nanoparticles (AuNPs) were initially deposited on the surface of gold electrode (GE) so as to get amplified electrochemical signals. Subsequently, a MIP film was created on the AuNPs modified GE (AuNPs/GE) surface by electropolymerization of o-aminophenol in the presence of AP as the template molecule. Significant parameters governing the performance of the sensor were studied and optimised. The proposed sensor presented a linear behaviour between peak current and concentration of AP in the range 4.5 × 10-5-5.0 × 10-7M with the limit of detection being 2.3 × 10-9M. The developed MIP/AuNPs/GE based sensor is simple in preparation and showed excellent selectivity, reproducibility and was successfully applied for the analysis of AP in pharmaceutical formulations and physiological fluids.

Biothiols induced colour change of silver nanoparticles: A colorimetric sensing strategy

A sensor for the detection and determination of bio-thiols (glutathione (GSH) and cysteamine (Cyste)) has been developed by integrating the distinguished distance related optical characteristics of silver nanoparticles with the simplicity of colorimetric technique. In presence of these analytes, shift in surface plasmon resonance (SPR) absorption of silver nanoparticles (AgNPs) with change in its colour was observed. Yellow coloured AgNPs solution becomes colourless in presence of GSH and changes to red in presence of Cyste. FTIR, TEM and DLS studies were used to confirm the mechanism. The difference in absorption of AgNPs in the absence and presence of GSH was found to vary linearly in the range 1.00×10-5M to 5.00×10-7M concentration range with limit of detection at 3.68×10-7M. The method can also be applied to quantify Cyste in the range 1.10×10-6M to 5.00×10-8M with limit of detection at 1.80×10-8M. The utility of the proposed colorimetric assay is validated by determination of GSH and Cyste in artificial blood serum.

Electrochemical determination of terazosin in pure form and in dosage forms

Two methods have been developed for the determination of terazosin in pure form and in dosage forms- one based on a potentiometric sensor and the other a voltammetric technique. Terazosin-silicotungstic acid ion-association is developed as an ionophore in the fabrication of the potentiometric sensor. The optimum concentration range of the developed method was 7 x 10^(-2) to 8 X 10^(-4) M of the drug. The system gave a perfectly Nernstian slope (59.3 mV per decade) in the pH 4.2 with hardly any interference from the common cations and anions. The cyclic and linear sweep voltammetric studies of the drug on a glassy carbon electrode in the potential range -100 to +100 mV with a switching potential of 800 mV have also been carried out. The drug gave a well-defined irreversible anodic peak at 774 mV when sodium hydroxide was used as the supporting electrolyte. Influence of scan rate and concentration on current were studied and based on this, a voltammetric method has also been developed for the quantitative determination of the drug. Both the methods have been applied for the determination of the drug in two commercially available tablets and the results are highly precise and accurate.

Fluorometric Determination of Epinephrine: A Green Approach.

Herein, a simple, sensitive and selective turn-on fluorescent method for the determination of epinephrine (EP), an important hormone and neurotransmitter, is described. The method is based on the interaction of EP with PEG6000 coated carbon nanoparticles (PCN) resulting in the fluorescence enhancement of PCN. A linear relationship was obtained between the fluorescence intensity and concentration of EP in the 9.90 × 10(-9) - 1.07 × 10(-7) M range; the detection limit being 7.59 × 10(-10) M. Furthermore, we demonstrated the application of the present approach in a synthetic urine sample, which suggested its great potential for diagnostic purposes.