A Novel Carbon Dot-Bromothymol Blue System for Ratiometric Colorimetric-Fluorometric Sensing of Glutathione in Urine: A Smartphone-Compatible Approach.

This study presents a novel dual-modal approach for glutathione (GSH) detection using blue and yellow dual-emission carbon dots (BY-CDs) and bromothymol blue (BTB) at pH 8.0. The method employs both colorimetric and fluorometric detection modes, offering a new perspective on GSH quantification. BTB's blue coloration induces selective fluorescence quenching of the CDs' 610 nm emission peak, with minimal effect on the 445 nm peak. Upon GSH addition, the quinonoid structure (blue color) of BTB transforms to its benzenoid form (yellow color). This transformation triggers fluorescence restoration at 610 nm and significant quenching at 445 nm, enabling ratiometric fluorescence analysis (F610/F445). Concurrently, colorimetric detection is also ratiometric, based on measuring the ratio between the emerging yellow color peak (435 nm) and the decreasing blue color peak (618 nm) (A435/A618). The state-of-the-art aspect of this detection method lies in the strategic choice of dual-emission CDs and a dye with distinct absorption spectra that closely match the emission spectra of the CDs. This unique combination allows for dual detection with opposite responses in the two detection modes, enhancing selectivity and reliability. The probe was thoroughly characterized, and its detection mechanism was elucidated using various spectroscopic techniques. The method shows excellent linearity, a broad detection range, and low detection limits for both fluorometry (0.02 - 10.0 µM, 5.88 nM) and colorimetry (1.0 - 35.0 µM, 301.25 nM). Additionally, a smartphone-based platform was developed for colorimetric GSH determination, enhancing the method's potential for on-site analysis. The assay's practicality was validated through successful application to human urine samples, yielding excellent recovery values (97.33% to 99.13%).

Sol-gel derived ceramic nanocomposite CNFs anchored with a nanostructured CeO2 modified graphite electrode for monitoring the interaction of a selective tyrosine kinase inhibitor capmatinib with dsDNA.

In the current study, the potential interaction mechanisms between capmatinib (CAP), a selective tyrosine kinase inhibitor, and calf thymus double-stranded DNA (ds-DNA) were evaluated. In this research, we construct an amplified electrochemical platform based on a disposable pencil graphite electrode (PGE) modified with nanostructured CeO2 decorated carbon nanofiber ceramic film (CeNPs@CNF-CF) for monitoring CAP-dsDNA interaction at physiological pH. The morphology and structure of the obtained CeNPs@CNF nanocomposite were characterized. The CeNPs@CNF-CF/PGE was characterized by scanning electron microscopy (SEM). The CAP-dsDNA interaction was examined using cyclic voltammetry (CV) and square wave voltammetry (SWV) techniques. Voltammetric experiments were conducted using CeNPs@CNF-CF/PGE. The interaction of CAP with dsDNA was investigated after applying different incubation times. The addition of dsDNA to the CAP solution decreased the peak currents of the latter and led to a negative shift in peak potentials, suggesting that the electrostatic type of interaction is the most likely to occur. SWV was employed to quantify dsDNA, demonstrating excellent sensitivity (LOD = 5 × 10-8 M). The binding constant (K b) of CAP and dsDNA was calculated to be 4.54 ± 0.18 × 104 M-1 using SW voltammetric data.

Electrochemical determination of captopril using a disposable graphite electrode modified with a molecularly imprinted film, accompanied by a ratiometric read-out.

In this research paper, a novel "signal on-off" ratiometric-based electrochemical platform was developed for the sensitive and selective detection of captopril. Ratiometric responses were achieved by fabricating molecularly imprinted polymers (MIPs) on the surface of a graphite electrode (GE) decorated with nitrogen (N) and sulfur (S) co-doped porous carbon and silver nanoparticles (Ag). The MIP layer was formed via electropolymerization of copper coordinated with pyrrole-3-carboxylic acid (functional monomer). Silver nanoparticles (Ag) were incorporated to enhance conductivity and surface area and to serve as an internal reference output. Upon the addition of captopril, there was a decrease in the anodic oxidation current of Ag+ at around 0.067 V, coupled with an increase in the oxidation current at 0.54 V (Ag-captopril complex). Under optimized conditions, the electrochemical responses (IAg-captopril/IAg) increased linearly with increasing captopril concentration in the range of 1-450 nM, with a detection limit (S/N = 3) of 0.3 nM. The ratiometric-based MIP electrochemical platform (Cu-MIP/NS-PC@Ag/GE) was successfully applied to detect captopril in complex matrices such as tablets, serum, and urine samples. This platform holds promise for sensitive and selective detection of captopril in various practical applications.

pH-Sensitive blue and red N-CDs for L-asparaginase quantification in complex biological matrices.

A novel fluorometric method for the determination of L-asparaginase, an enzyme crucial in cancer therapy and food industry applications, is presented. This sensitive and selective approach utilizes L-asparagine and two pH-sensitive carbon dots (blue-N-CDs and red-N-CDs) as probes. The interaction between L-asparagine and L-asparaginase liberates ammonia, causing an increase in pH. This pH change simultaneously decreases the fluorescence of blue-N-CDs while enhancing the emission of red-N-CDs, enabling ratiometric detection of L-asparaginase. Comprehensive characterization of both carbon dots and investigation of their response mechanism towards L-asparaginase were conducted using ultraviolet-visible spectrophotometry, fluorescence spectroscopy, and transmission electron microscopy (TEM) imaging techniques. The designed approach demonstrates outstanding linearity (20 to 2000 U L-1) and a low detection limit (6.95 U L-1) for L-asparaginase quantification. Moreover, when tested to human serum samples, the detection system exhibits outstanding selectivity and high recovery rates (96.15% to 99.75%) with low standard deviation, underscoring its suitability for practical implementation in clinical diagnostics.

L-asparaginase-mediated pH shift and carbon dot fluorescence modulation: A sensitive ratiometric method for quantifying L-asparagine in diverse potato varieties under variable storage conditions.

This study presents a novel and selective method for the determination of l-asparagine in diverse potato varieties under various storage conditions. L-asparagine levels serve as a crucial indicator for acrylamide formation, a hazardous substance in processed potato products. The fluorometric method utilized blue-emitting CDs (B-CDs), orange-emitting CDs (O-CDs), and the enzyme L-asparaginase for ratiometric detection of L-asparagine. Upon enzymatic hydrolysis of L-asparagine by L-asparaginase, liberated ammonia induced a pH increase in the reaction medium. This pH shift enhanced the fluorescence of B-CDs while simultaneously decreasing that of O-CDs, enabling sensitive and selective L-asparagine quantification. Comprehensive characterization of the CDs was performed using various spectroscopic techniques and transmission electron microscopy. The method demonstrated excellent sensitivity (LOD = 0.31 µM) and a wide linear range (1.0-50.0 µM). When the method was applied to potato samples, high recovery values (98.00-100.33 %) with low relative standard deviations (RSDs) were achieved, confirming the accuracy and precision of the method. The approach was employed to determine L-asparagine levels in three potato varieties (Lady Rosetta, Spunta, and Nicola) under different storage temperatures and durations. This method provides a valuable tool for monitoring L-asparagine content in potatoes, potentially aiding in the mitigation of acrylamide formation during processing. The robust performance and simplicity of the proposed technique make it suitable for routine analysis in both research and industrial applications within the potato industry.

A novel urease-assisted ratiometric fluorescence sensing platform based on pH-modulated copper-quenched near-infrared carbon dots and methyl red-quenched red carbon dots for selective urea monitoring.

A novel and sensitive fluorescence ratiometric method is developed for urea detection based  on the pH-sensitive response of two fluorescent carbon dot (CD) systems: R-CDs/methyl red (MR) and NIR-CDs/Cu2+. The sensing mechanism involves breaking down urea using the enzyme urease, releasing ammonia and increasing pH. At higher pH, the fluorescence of NIR-CDs is quenched due to the enhanced interaction with Cu2+, while the fluorescence of R-CDs is restored as the acidic MR converts to its basic form, removing the inner filter effect. The ratiometric signal (F608/F750) of the R-CDs/MR and NIR-CDs/Cu2+ intensities changed in response to the pH induced by urea hydrolysis, enabling selective and sensitive urea detection. Detailed spectroscopic and morphological investigations confirmed the fluorescence probe design and elucidated the sensing mechanism. The method exhibited excellent sensitivity (0.00028 mM LOD) and linearity range (0.001 - 8.0 mM) for urea detection, with successful application in milk samples for monitoring adulteration, demonstrating negligible interference and high recovery levels (96.5% to 101.0%). This ratiometric fluorescence approach offers a robust strategy for selective urea sensing in complicated matrices.

A novel disposable ultrasensitive sensor based on nanosized ceria uniformly loaded carbon nanofiber nanoceramic film wrapped on pencil graphite rods for electrocatalytic monitoring of a tyrosine kinase inhibitor capmatinib.

For the first time, we introduce a novel disposable and ultrasensitive sensing electrode made up of nanosized ceria uniformly loaded carbon nanofibers (CeNPs@CNF) sol-gel nanoceramic film (CF) wrapped on eco-friendly and inexpensive pencil graphite rods (PGRs) to explore their electro-catalytic detection of the anticancer drug capmatinib (CMB). The as-prepared CeNPs@CNF hybrid nanocomposite was described by XRD, SEM, TEM, HRTEM, and EDX analysis. The CV study clearly demonstrated that, the disposable CeNPs@CNF-CF/PGRE sensor exhibited excellent redox activities in the ideal probe [Fe(CN)6]3-/4-. Due to the outstanding electrochemical properties, larger electrochemically active surface area, and tremendous electro-catalytic activity of CeNPs@CNF, the reduction current of CMB on the CeNPs@CNF-CF/PGRE sensor is considerably higher than that of bare PGRE. The detection conditions, such as supporting electrolyte, pH of the buffer solution, amount of modifier, adsorption potential, and time, were studied and optimized. The sensing platform demonstrated high sensitivity (1.2 µA nM-1 cm-2), an ultralow detection limit (0.6 nM), and a wide linear range of 2.0 nM-400 nM of CMB compared to the bare PGRE. Additionally, the CeNPs@CNF-CF/PGRE sensor showed high selectivity, stability, and simple operation, which provided a promising alternative tool for fast detection of CMB in human body fluids with good recoveries.

Enhanced fluorescent detection of oxaliplatin via BSA@copper nanoclusters: a targeted approach for cancer drug monitoring.

A new fluorescence sensing approach has been proposed for the precise determination of the anti-cancer drug oxaliplatin (Oxal-Pt). This method entails synthesizing blue-emitting copper nanoclusters (CuNCs) functionalized with bovine serum albumin (BSA) as the stabilizing agent. Upon excitation at 360 nm, the resultant probe exhibits emission at 460 nm. Notably, the fluorescence response of BSA@CuNCs substantially increases upon incubation with Oxal-Pt due to multiple binding interactions between the drug and the fluorescent probe. These interactions involve hydrogen bonding, hydrophobic interaction, and the high affinity between the SH groups (cysteine residues of BSA) and platinum (in Oxal-Pt). Consequently, this interaction induces aggregation-induced emission enhancement (AIEE) of BSA@CuNCs. The probe demonstrates a broad response range from 0.08 to 140.0 µM, along with a low detection limit of 20.0 nM, determined based on a signal-to-noise ratio of 3. Furthermore, the probe effectively detects Oxal-Pt in injections, human serum, and urine samples, yielding acceptable results. This study represents a significant advancement in the development of a straightforward and efficient sensor for monitoring platinum-containing anti-cancer drugs during chemotherapy.

Surface engineering of carbon microspheres with nanoceria wrapped on MWCNTs: a dual electrocatalyst for simultaneous monitoring of molnupiravir and paracetamol.

In the present study, nanoceria-decorated MWCNTs (CeNPs@MWCNTs) were synthesized using a simple and inexpensive process. Molnupiravir (MPV) has gained considerable attention in recent years due to the infection of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Since some people infected with COVID-19 experience fever and headaches, paracetamol (PCM) has been prescribed to relieve these symptoms. Therefore, there is an urgent need to monitor and detect these drugs simultaneously in pharmaceutical and biological samples. In this regard, we developed a novel sensor based on nanoceria-loaded MWCNTs (CeNPs@MWCNTs) for simultaneous monitoring of MPV and PCM. The incorporation of CeNPs@MWCNTs electrocatalyst into a glassy carbon microsphere fluorolube oil paste electrode (GCMFE) creates more active sites, which increase the surface area, electrocatalytic ability, and electron transfer efficiency. Interestingly, CeNPs@MWCNTs modified GCMFE demonstrated excellent detection limits (6.0 nM, 8.6 nM), linear ranges (5.0-5120 nM, 8.0-4162 nM), and sensitivities (78.6, 94.3 µA µM-1 cm-2) for simultaneous detection of MPV and PCM. The developed CeNPs@MWCNTs electrocatalyst modified GCMFE exhibited good repeatability, anti-interference capability, stability, and real-time analysis with good recovery results, which clearly indicates that it can be used for real-time industrial applications.

Synergistic effect of gold nanoparticles anchored on conductive carbon black as an efficient electrochemical sensor for sensitive detection of anti-COVID-19 drug Favipiravir in absence and presence of co-administered drug Paracetamol.

Favipiravir (FVP) is introduced as a promising newly developed antiviral drug against the coronavirus disease 2019 (COVID-19). Therefore, the accurate determination of FVP is of great significance for quality assessment and clinical diagnosis. Herein, a novel electrochemical sensing platform for FVP based on gold nanoparticles anchored conductive carbon black (Au@CCB) modified graphite nanopowder flakes paste electrode (GNFPE) was constructed. Morphological and nanostructure properties of Au@CCB have been investigated by TEM, HRTEM, and EDX methods. The morphology and electrochemical properties of Au@CCB/GNFPE were characterized by SEM, cyclic voltammetry (CV), and EIS. The Au@CCB nanostructured modified GNFPE exhibited strong electro-catalytic ability towards the oxidation of FVP. The performance of the fabricated Au@CCB/GNFPE was examined by monitoring FVP concentrations in the absence and presence of co-administered drug paracetamol (PCT) by AdS-SWV. It was demonstrated that the proposed sensor exhibited superior sensitivity, stability, and anti-interference capability for the detection of FVP. The simultaneous determination of a binary mixture containing FVP and the co-administered drug PCT using Au@CCB/GNFPE sensor is reported for the first time. Under optimized conditions, the developed sensor exhibited sensitive voltammetric responses to FVP and PCT with low detection limits of 7.5 nM and 4.3 nM, respectively. The sensing electrode was successfully used to determine FVP and PCT simultaneously in spiked human plasma and pharmaceutical preparations, and the findings were satisfactory. Finally, the fabricated sensor exhibited high sensitivity for simultaneous detection of FVP and PCT in the presence of ascorbic acid in a real sample.

Bifunctional ratiometric sensor based on highly fluorescent nitrogen and sulfur biomass-derived carbon nanodots fabricated from manufactured dairy product as a precursor.

Novel biomass-derived carbon dots co-doped with nitrogen and sulfur were fabricated through facile and simple synthetic method from manufactured milk powder and methionine as precursors. The as-fabricated platform was used for ratiometric fluorescence sensing of Cu (II) and bisphosphonate drug risedronate sodium. The sensing platform is based on oxidation of o-phenylenediamine by Cu (II) to form 2, 3-diaminophenazine (oxidized product) with an emission peak at 557 nm. The resultant product quenched the fluorescence emission of as-fabricated carbon dots at 470 nm through Förster resonance energy transfer (FRET) and inner-filter effect (IFE). Upon addition of risedronate sodium, the formation of 2, 3-diaminophenazine was decreased as a result of Cu (II) chelation with risedronate sodium, recovering the fluorescence emission of carbon dots. The ratio of fluorescence at 470 nm and 557 nm was measured as a function of Cu (II) and risedronate sodium concentrations. The proposed sensing platform sensitively detected Cu (II) and risedronate sodium in the range of 0.01-55 µM and 5.02-883 µM with LODs (S/N = 3) of 0.003 µM and 1.48 µM, respectively. The sensing platform exhibited a good selectivity towards Cu (II) and risedronate sodium. The sensing system was used to determine Cu (II) and risedronate sodium in different sample matrices with recoveries % in the range of 99-103 % and 97.4-103.8 %, and RSDs % in the range of 1.5-3.0 % and 1.8-3.6 %, respectively.

A new hybrid nanocomposite electrode based on Au/CeO2-decorated functionalized glassy carbon microspheres for the voltammetric sensing of quercetin and its interaction with DNA.

A new hybrid composite containing cerium oxide nanoparticle (CeO2NP) and gold nanoparticle (AuNP)-decorated functionalized glassy carbon microspheres (FGCM) was synthesized (Au/CeO2@FGCM). As a result, an Au/CeO2@FGCM-paraffin oil paste electrode (PE) (Au/CeO2@FGCM-PE) was fabricated and employed for the voltammetric sensing of quercetin (QRT). The structure and surface morphology of Au/CeO2@FGCM were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Cyclic voltammetry (CV), square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS) were employed for the investigation of the electrochemical behavior of Au/CeO2@FGCM-PE. Under the optimum conditions, the SWV oxidation peak current showed linear dependence on the QRT concentration in the range from 48 nM to 1.09 µM. The achieved limits of detection and quantitation were 0.37 nM and 1.22 nM, respectively. Au/CeO2@FGCM-PE was reproducible, sensitive and stable and displayed anti-interference ability for various common interferents. The proposed method was also successfully applied for real sample analysis. The QRT content extracted from natural sources was determined, and satisfactory results were achieved. Furthermore, the interaction of QRT with salmon testes and calf thymus dsDNA (st-DNA and ct-DNA) on Au/CeO2@FGCM-PE was studied by CV and SWV. The corresponding binding constant (K), surface concentration (Γ), and Gibbs free energy (ΔG°) were computed for the free QRT and the bound QRT-dsDNA complex. The calculated K values for the QRT-ct-DNA and QRT-st-DNA complexes were found to be 6.24 × 105 M-1 and 3.63 × 105 M-1, respectively, which revealed that QRT strongly interacted with ct-DNA compared to that with st-DNA. The decreased intensity of the QRT oxidation peak resulting from its interaction with dsDNA provides a chance to use QRT as a new indicator to analyze ct-DNA and st-DNA.

Gold nanoparticles anchored graphitized carbon nanofibers ionic liquid electrode for ultrasensitive and selective electrochemical sensing of anticancer drug irinotecan.

An electrochemical sensor is described for highly sensitive and selective determination of anticancer drug irinitecan (IRT). Gold nanoparticles anchored graphitized carbon nanofibers (Au@GCNFs) was prepared. Au@GCNFs was characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray. The combination of high catalytic activity of the nanocomposite Au@GCNFs and the good conductivity ionic liquid [BMIM]PF6 (IL) resulted in a modified paste electrode (IL/Au@GCNFs-PE). The IL/Au@GCNFs-PE exhibits excellent electrocatalytic activity for selective determination of IRT in the presence of physiological electroactive species, such as ascorbic acid (AA), dopamine (DA), uric acid (UA), and caffeine (CAF) mixture, typically at working potential of 0.88 V vs. Ag/AgCl. The linear response ranges 4.0 nM-1.79 µM and 4.5 nM-1.57 µM with limits of detection of 1.55 nM and 1.70 nM were calculated for IRT in the absence and presence of the quaternary mixture, respectively. The sensor is reproducible and stable over four weeks, and interference by biologically essential compounds is negligible. The method was applied to the determination of IRT in pharmaceutical formulations, in spiked blood serum and urine, and in clinical patient blood. The recovery values ranged from 96.0 to 104.2%. Graphical abstract The combination of high catalytic activity of the new nanocomposite AuNPs@GCNFs with the good conductivity ionic liquid (IL) resulted to a modified paste electrode (IL/Au@GCNFs-PE). The novel sensor was successfully applied for the sensitive and selective detection of IRT in biological samples in the presence of quaternary ascorbic acid (AA), dopamine (DA), uric acid (UA), and caffeine (CAF) mixture.

Exploring efficacy of indole-based dual inhibitors for α-glucosidase and α-amylase enzymes: In silico, biochemical and kinetic studies.

α-Glucosidase and α-amylase are enzymes which are associated with diabetic II. These enzymes break macromolecules of sugar into monosugar molecules which is soluble in body, hence increase the sugar level in blood. There is need to develop economical and save inhibitors to prevent them from breaking sugar macromolecules to soluble molecules which will control the level of sugar in blood. Therefore, we synthesized indole-based derivatives (1-18) and evaluated as dual inhibitor for α-glucosidase and α-amylase. These chemical scaffolds were built with variation in aryl ring which were found active with good to moderate activity for α-glucosidase having IC50 value ranging from 13.99 ± 0.10 to 59.09 ± 0.30 µM when compared with standard acarbose with IC50 of 11.29 ± 0.10 µM; for α-amylase IC50 value ranging from 13.14 ± 0.10 to 58.99 ± 0.30 µM when compared with the standard acarbose with IC50 of 11.12 ± 0.10 µM. Structure activity relationship (SAR) has been established for all compounds. Enzymatic kinetic study and molecular docking study have been carried out to investigate the binding interactions α-glucosidase and α-amylase enzyme.

Synergistic electrocatalytic activity of In2O3@FMWCNTs nanocomposite for electrochemical quantification of dobutamine in clinical patient blood and in injection dosage form.

Dobutamine (DBT) is a sympathomimetic amine drug that was designed as an inotropic agent for use in congestive heart failure. Hence, there was an impetus to develop a rapid and accurate method for monitoring the concentration of DBT within clinical samples. To address this critical need, a novel In2O3 and functionalized multi-walled carbon nanotubes nanocomposite (In2O3@FMWCNTs) was successfully prepared and applied in an electrochemical sensor to detect DBT. The resulting sensor displayed electrocatalytic toward the oxidation of DBT, which attributed to the synergistic effect of In2O3 and FMWCNTs. Electrochemical impedance spectroscopy (EIS) studies revealed that the smaller charge transfer resistance value (Rct) was observed at In2O3@FMWCNTs modified glassy carbon spherical (GCS) paste electrode (PE) as compared to that of In2O3NPs/GCSPE, FMWCNTs/GCSPE and GCSPE, which authenticates its good conductivity. Furthermore, the calculated value of standard rate constant (ks) for the modified electrode demonstrates the fast electron transfer between DBT and the electrode surface. The fabricated electrochemical sensor indicated high selectivity and sensitivity for DBT determination over the oxidation of uric acid and ascorbic acid. The limit of detection of DBT at In2O3@FMWCNTs/GCSPE was found to be 1.42 × 10-10 M. The proposed sensor is effectively used for the detection of DBT in biological fluids, clinical patient blood and in injection dosage form.

A novel megestrol acetate electrochemical sensor based on conducting functionalized acetylene black-CeO2NPs nanohybrids decorated glassy carbon microspheres.

For the first time, megestrol acetate (MGA), a synthetic progestin with therapeutic use in breast cancer, is electrochemically studied to propose a new electroanalytical alternative for its detection in real samples. In the present work, a novel electrochemical sensor based on functionalized acetylene black-CeO2NPs nanohybrids modified glassy carbon microspheres paste electrode (FAB-CeO2NPs/GCMPE) was successfully fabricated and used for sensitive determination of MGA. The modified electrode has been characterized using scanning electron microscope (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The electrocatalytic reduction of MGA using FAB-CeO2NPs/GCMPE was carried out via CV and square wave voltammetry (SWV). By employing FAB-CeO2NPs/GCMPE, the SWV signal of MGA reduction was 8 fold higher than the bare GCMPE. A wide concentration range from 4.20 × 10-8 to 1.13 × 10-6 M with the low LOD of 1.30 nM for MGA was achieved. The practical analytical utilities of the prospective FAB-CeO2NPs/GCMPE sensor were demonstrated successfully by the detection of MGA in Megace tablets, human serum and urine samples obtained from healthy and patient volunteers after oral administration of 160 mg Megace tablets. HPLC method was also developed for comparison with the electroanalytical method.

A hybrid nanocomposite of CeO2-ZnO-chitosan as an enhanced sensing platform for highly sensitive voltammetric determination of paracetamol and its degradation product p-aminophenol.

For the determination of paracetamol (PAR) and its primary degradation product (p-aminophenol, PAP) a highly selective electrochemical sensor was fabricated. A glassy carbon microspheres paste electrode (GCMPE) was modified with a CeO2-ZnO-chitosan hybrid nanocomposite (CeO2-ZnO-CS) which was characterized by X-ray diffraction and transmission electron microscopy. The CeO2-ZnO-CS/GCMPE was characterized by scanning electron microscopy, and cyclic voltammetry. The modified GCMPE exhibits excellent electrocatalytic activity for the determination of PAR and PAP separately or simultaneously, typically at working potentials of 0.38 and 0.09 V vs. Ag/AgCl. The square wave voltammetric response in solutions of near-neutral pH value increases linearly in the 20 nM to 1.8 µM PAR concentration range, and the lower LOD is 0.86 nM. The sensor is shown to enable the determination of PAR even in the presence of a 180-fold excess of PAP. PAR and PAP can also be simultaneously determined, and the LODs for PAR and PAP are 0.98 nM and 9.5 nM, respectively. The results agreed well with data obtained using other electrodes. The sensor is reproducible and stable over eight weeks, and interference by biologically essential compounds is negligible. The method was applied to the determination of PAR in pharmaceutical formulations and in spiked blood serum and urine samples. The relative standard deviations ranged from 97.5 to 102.0%.

A novel sensor based on nanobiocomposite Au--In2O3--chitosan modified acetylene black paste electrode for sensitive detection of antimycotic ciclopirox olamine.

For the first time, a sensitive conductive nanobiocomposite sensor consisting of Au-In2O3 nanocomposite and chitosan (CS) was successfully prepared and used for the modification of acetylene black paste electrode (Au--In2O3--CS/ABPE). The phase structures, composition and morphology of Au-In2O3 nanocomposite were characterized by X-ray diffraction (XRD), energy-dispersed X-ray (EDX) and transmission electron microscopy (TEM). Electrochemical activities and surface analysis of the biosensor electrode Au--In2O3--CS/ABPE were investigated using scanning electron microscopy (SEM), cyclic voltammetry and square wave voltammetry. The modified electrode showed an excellent electrochemical activity toward the electro-oxidation of the antimycotic ciclopirox olamine (CPX) leading to a significant improvement in sensitivity as compared to the bare ABPE. The proposed biosensor demonstrated linearity in the range 0.199 - 16.22µmolL-1, with high sensitivity (64.57µAµmolL-1cm-2) and detection limit of 6.64 × 10-9molL-1 CPX. The analytical performance of this biosensor was evaluated for detection of CPX in pharmaceutical formulations with good accuracy and precision. This proposed method was validated by UPLC and the results are in agreement at the 95% confidence level.

Comparative studies on the interaction of anticancer drug irinotecan with dsDNA and ssDNA.

A systematic comparative study on the binding of anticancer drug irinotecan (Irino) with dsDNA and ssDNA was investigated in phosphate buffer solutions using voltammetric and spectroscopic methods. The voltammetric results show that the Irino molecule, acting as an intercalator, is inserted into the base stacking domain of the DNA double helix and the strength of interaction is independent of the ionic strength. The hyperchromic effect observed in the UV-visible spectra of Irino in the presence of dsDNA provided the evidence for the intercalation of the drug chromophore with dsDNA base. The interaction mode of Irino molecules with ssDNA is electrostatic attraction via negative phosphate on the exterior of the ssDNA with Irino. The binding constants, stoichiometric coefficients and thermodynamic parameters of Irino-dsDNA and Irino-ssDNA complexes were evaluated. The magnitude of changes in ΔG o, ΔH o and ΔS o indicated that the binding process of Irino with ssDNA was more affected than that with dsDNA. The decrease of the peak current of Irino was proportional to DNA concentration, which was applied for determination of dsDNA and ssDNA concentration. The achieved limits of detection of dsDNA and ssDNA were 5.49 × 10-7 and 1.87 × 10-7 M, respectively.

Binding mode and thermodynamic studies on the interaction of the anticancer drug dacarbazine and dacarbazine-Cu(II) complex with single and double stranded DNA.

The binding mode and thermodynamic characteristics of the anticancer drug dacarbazine (Dac) with double and single stranded DNA were investigated in the absence and presence of Cu(II) using cyclic voltammetry, square wave voltammetry and fluorescence spectroscopy. The interaction of Dac and Dac-Cu(II) complex with dsDNA indicated their intercalation into the base stacking domain of dsDNA double helix and the strength of interaction is independent on the ionic strength. The interaction of Dac with dsDNA in the presence of Cu(II) leads to a much stronger intercalation. The interaction mode of Dac molecules with ssDNA is electrostatic attraction via negative phosphate on the exterior of the ssDNA with Dac. The binding constants, stoichiometric coefficients and thermodynamic parameters of Dac and Dac-Cu(II) complex with dsDNA and ssDNA were evaluated. Comparison of the mode interaction of Dac with dsDNA and ssDNA was discussed. The decrease of peak current of Dac was proportional to DNA concentration, which was applied for determination of dsDNA and ssDNA concentration.