Wide Linear Dynamic Range Research Articles

Electrocatalytic investigation of H2O2 reduction and sensing performance using sulfide modified Au/Pt electrode in alkaline medium

Hydrogen peroxide (HP) is extensively utilized in numerous industries for synthesizing various chemicals and as a fueling vector in direct peroxide fuel cells in place of oxygen molecules. Therefore, it is crucial to detect HP quickly and develop a cost-effective method for this purpose. The Au/Pt electrode surface exhibits no substantial electrocatalytic activity towards HP reduction reaction, although facilitates oxygen reduction reaction (ORR). To address this issue, in this work, S2- ions have been partially immobilized on Au/Pt surface (termed as [sub-S-Au/Pt]). This modified electrode eliminated catalytic sites for oxygen reduction and generated catalytic sites for facilitating the HP reduction reaction. Comprehensive electrochemical investigations and characterizations of the developed sensor were carried out using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), open circuit potential (OCP), chronoamperometry, and Differential pulse voltammetry (DPV) techniques. The relationship between the current response and HP concentration exhibited a wide linear dynamic range (LDR) ranging from 2 to 1500 μM, with a limit of detection (LOD) of 2.3 μM. The sensitivity of the sensor was determined to be 423.7 μA mM−1cm−2. Additionally, this article provides insight into the kinetics of the HP reduction reaction using the [sub S-Au/Pt] electrode in an alkaline medium. The modified electrode surface was characterized using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS).

Self-powered photodetector based on a CsPbBr3/n-Si Schottky junction

Self-powered photodetectors (SPPDs) are attracting considerable publicity due to their superiority over conventional photodetectors (PDs) in terms of high sensitivity, fast response, and no need for an external power supply. Halide perovskites are much anticipated in SPPDs for their unusual photoelectronic properties. This work developed a Schottky junction CsPbBr3/n-Si SPPD by growing stable all-inorganic CsPbBr3 microcrystals on an n-Si substrate using a solution method. At zero bias, such Schottky SPPD has a very weak dark current (0.3 pA), a wide linear dynamic range (LDR, 110 dB), a sizeable on–off ratio (>103), and high detectivity (1.05×1011Jones). Through the research of this project, it is expected to obtain a way to prepare Schottky photodiodes with high stability and self-driving capability.

Electrostatic Nanocage-Confined Probe for Electrochemical Detection of CA19-9 in Human Serum.

Prompt and accurate detection of CA19-9 in human serum has great clinical significance for the early diagnosis and disease monitoring of cancer. Herein, we develop a convenient and antifouling electrochemical sensor for CA19-9 determination by immobilization of both an electrochemical redox probe [methylene blue (MB)] and immunorecognition element (CA19-9 antibody) on an electrostatic nanocage consisting of bipolar silica nanochannel array (bp-SNA). bp-SNA is composed of a negatively charged inner layer (n-SNA) and positively charged outer layer (p-SNA), which could be stably prepared on indium tin oxide (ITO) in several seconds using a two-step electrochemically assisted self-assembly approach and display asymmetric surface charges for confinement and enrichment of cationic MB into the inner n-SNA layer through electrostatic interaction. Modification of the CA19-9 antibody on the top surface of bp-SNA confers the sensing interface with specific recognition capacity. An antibody-antigen complex formed at the as-prepared immunosensor causes the decreased electrochemical signals of MB, achieving sensitive determination of CA19-9 with a wider linear dynamic range from 10 μU/mL to 50 U/mL and a low detection limit (3 μU/mL). Furthermore, accurate and feasible analysis of the CA19-9 amount in human serum samples by our proposed probe-integrated electrochemical immunosensor is realized.

Decay-Associated Fluorescence for Boron Determination in Uranium-Based Nuclear Fuels.

Herein is reported a novel as well as simple, sensitive, and cost-effective method for determination of boron by time-resolved fluorescence spectrometry in uranium-based nuclear fuels. Boron is complexed with fluorescent ligand chromotropic acid, and the complex formed is a measure of boron. Since the steady-state fluorescence spectra of excess ligand and complex are overlapping, the developed method emphasizes the power of time resolution. The signatory fluorescence decay times of ligand and complex are employed to derive their decay-associated spectra (DAS) and, thereby, spectroscopically eliminate the high background of ligand fluorescence. The calibration plot has a wide linear dynamic range of 5-100 ppb with r2 better than 0.998. Precision is better than 5% at the 10 ppb level and 4% at the 50 ppb level (n = 9). The detection limit is 1.5 ppb, and recovery of spiked boron (25 ppb) from the uranium samples was better than 94%. The developed method was validated by analyzing U3O8-based ILCE Standards and applied to enriched uranium fuel samples. The main advantage of the developed method is a reduction in sample size requirement due to better sensitivity and selectivity. This in turn reduces the load of uranium recovery from analytical waste, especially in the case of enriched uranium samples. Additionally, it eliminates the need of organic solvents/medium.

Voltammetric analysis of mephenoxalone drug in pharmaceutical and biological samples using novel screen-printed sensor with boron-doped diamond electrode

A novel screen-printed sensor (SPE) with boron-doped diamond electrode (BDDE) for determination of a muscle relaxant and mild anxiolytic mephenoxalone (MNL) was developed. The sensor utilizes the electrochemical oxidation of MNL, which was firstly studied in aqueous solution using oxygen terminated BDDE. MNL provided an irreversible anodic signal at a potential of + 1380 mV (vs. Ag/AgCl/KCl sat.) over a wide pH range. Britton-Robinson buffer (pH 9) was selected as a suitable electrolyte and the square-wave voltammetric method (SWV) was developed. The low detection limit (55 nmol L–1), wide linear dynamic range (0.1–30 µmol L−1), and good recovery in the analysis of model and pharmaceutical samples (RSD < 1.77%) were attained. Subsequently, the new method was successfully transferred to SPE, which can find application in point-of-care testing. These sensors proved excellent sensitivity and reproducibility in the analysis of biological samples (RSD < 4.94%) without pretreatment and no need of electrolyte. Based on gas chromatography with mass spectrometry (GC-MS) analysis of preparative electrolysis products, a mechanism of the electrochemical oxidation of MNL was proposed, describing the oxidative cleavage of the alkoxybenzene ring. These results were supported with HOMO spatial distribution calculations and atomic charges calculations for arising radical cations, and with spectroelectrochemical measurements.

Electrostatically-driven self-assembly of copper nanoclusters and carbon dots for quantitative protamine and heparin determination

A novel nanosystem composed of red-emissive thiolate-capped copper nanoclusters (GSH-CuNCs) and blue-emissive polyethyleneimine-tailored carbon dots (B-CDs+) was utilized for the quantitative determination of protamine and heparin. Addition of B-CDs+ to a solution containing GSH-CuNCs resulted in a significant increase in the fluorescence emission of GSH-CuNCs due to their self-assembly through an electrostatic interaction. However, in the presence of protamine, a polycationic protein, the fluorescence emission of GSH-CuNCs at 590 nm was decreased as a result of adsorbing protamine on GSH-CuNCs surface instead of B-CDs+. This led to disassembling of GSH-CuNCs, while the fluorescence emission of B-CDs+ at 470 nm remained unchanged during the determination. In the presence of heparin, a negatively charged molecule, the fluorescence emission of GSH-CuNCs nanosystem was recovered due to strong electrostatic interaction between protamine and heparin. The displaced B-CDs+ aggregated the GSH-CuNCs, restoring its fluorescence emission. Under optimized conditions, the fluorescence responses were increased with the protamine and heparin concentrations in the range of 0.004–40 µg/mL and 0.01–28 µg/mL, with LODs (S/N = 3) of 0.001 µg/mL and 0.004 µg/mL, respectively. The nanosystem offers several merits, including an ultra-low LODs, wide dynamic linear range, good anti-interference, satisfactory detection reliability, and short response time. Importantly, this strategy was successfully devoted to estimate protamine and heparin in urine and serum samples, and the results were found to be acceptable.

Topological Darkness: How to Design a Metamaterial for Optical Biosensing with Ultrahigh Sensitivity.

Due to the absence of labels and fast analyses, optical biosensors promise major advances in biomedical diagnostics, security, environmental, and food safety applications. However, the sensitivity of the most advanced plasmonic biosensor implementations has a fundamental limitation caused by losses in the system and/or geometry of biochips. Here, we report a "scissor effect" in topologically dark metamaterials which is capable of providing ultrahigh-amplitude sensitivity to biosensing events, thus solving the bottleneck sensitivity limitation problem. We explain how the "scissor effect" can be realized via the proper design of topologically dark metamaterials and describe strategies for their fabrication. To validate the applicability of this effect in biosensing, we demonstrate the detection of folic acid (vitamin important for human health) in a wide 3-log linear dynamic range with a limit of detection of 0.22 nM, which is orders of magnitude better than those previously reported for all optical counterparts. Our work provides possibilities for designing and realizing plasmonic, semiconductor, and dielectric metamaterials with ultrasensitivity to binding events.

Competitive Assay for the Ultrasensitive Detection of Organophosphate Pesticides Based on a Fiber-Optic Particle Plasmon Resonance Biosensor and an Acetylcholinesterase Binding Peptide.

An acetylcholinesterase (AChE) binding-based biosensor was developed for the ultrasensitive detection of organophosphate (OP) pesticides. The biosensor integrates the technique based on fiber-optic particle plasmon resonance detection and a synthetic AChE binding peptide conjugated with gold nanoparticles on the optical fiber surface via an AChE competitive binding assay. The OP pesticides present in the solution hinder the binding of AChE to the peptide on the biosensor by competing for the binding sites present in AChE. The limit of detection obtained for parathion using this method was observed to be 0.66 ppt (2.3 pM). This method shows a wide linear dynamic range of 6 orders. Furthermore, the use of the AChE binding peptide in the biosensor can better discriminate OPs against carbamates by using only a single biosensor. The practical application of this method was tested using spiked samples, which yielded good recovery and reproducibility. The spiked sample required minimal pretreatment before analysis; hence, this biosensor may also be used in the field.

Investigating hazardous 4-aminoantipyrine with functionalized Eco-friendly Fe3O4 nanoparticles decorated nontoxic Molybdenum disulfide nanosheet sensor

In the current study, a new sensor for sensing AAP in pH 3.0 is being developed employing Hydrocerol-A coated green magnetite nanoparticle (HCA-Fe3O4) wrapped MoS2 nanocomposite modified glassy carbon electrode (HCA-Fe3O4/MoS2@GCE). The electrode material was characterized by CV, SEM, EDX, XRD, and EIS. The proposed sensor showed strong electrocatalytic activity and electrooxidation towards 4-aminoantipyrine with higher peak shift compared to the bare electrode. A plausible mechanism has been suggested to account for the participation of protons and electrons in the oxidation reaction of 4-aminoantipyrine. The quantification of the sensor was conducted using SWV studies under optimized conditions. The obtained results demonstrated that the sensor exhibited a low limit of detection of 9.8 nM and a quantification limit of 30 nM. Additionally, the sensor displayed a wide linear dynamic range spanning from 0.08 to 20 μM. The sensor that was developed demonstrated favorable selectivity for the electrochemical detection of AAP, even in the presence of interferants. Moreover, the artificially created sensor was evaluated for its feasibility in contaminated biological and water samples.

Self-signal generating bioelectronic sensor surface using gadolinium hexacyanoferrate nanocomposite for oral cancer diagnosis

External redox reagents and chemical mediators in measuring solutions are extensively used to monitor the analytical signals in electrochemical immunosensors. These mediators add more steps and complications to the sensing procedures which are aggravated when testing the target molecule in real samples. Thus, it is important to resolve such issues by fabricating and engineering sensitive electroactive surfaces without the requirement of mediators in the solution phase. In this work, we report a self-reporting electrochemical biosensor for cyfra-21–1 detection in saliva samples without using any external mediator molecules in solution phase. To fabricate an electrochemically active surface, a redox active Gadolinium hexacyanoferrate (GdHCF) nanoparticles have been synthesized and deposited onto the electrode surface for label-free detection of cyfra-21–1 in combination with gold nanoparticles (AuNP) and graphene oxide (GO). The sensor probe was thoroughly characterized using X-ray diffraction (XRD), UV–vis spectroscopy, transmission electron microscopy (TEM), Raman Spectroscopy, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). An alternation in the protein biomarker concentrations led to a change in the current response of the electrode surface. differential pulse voltammetry (DPV) was used to establish the analytical performance of the fabricated biosensor. The sensor achieved a clinically relevant range as well as a wide linear dynamic range (LDR) of 2–50 ng/mL of cyfra-21–1 and a detection limit (DL) of 0.039 ( ± 0.01) ng/mL ((RSD < 4.12%, 95% confidence level, n = 3), with negligible interferences effect due to various co-existing molecules. This is the first-ever report where a redox-active surface has been fabricated comprising GdHCF for direct detection of cyfra-21–1 in human saliva samples without using any redox mediator in the solution phase.

Electrochemical determination of Vitamin B6 using coral-like MnO2-Pi on Ti3C2Tx MXene

MXenes are 2D nanomaterials that are considered the materials of the future generation due to their high electrical conductivity, good biocompatibility, and ease of functionalization. This research work reports the electrochemical sensing of Vitamin B6 using the Manganese dioxide-inorganic phosphate/MXene brush-coated Carbon fiber paper electrode (MnO2-Pi/MXene/CFP) electrode for the first time. The three-dimensional Ti3C2Tx MXene nanosheets consisting of highly ordered, vertically aligned nanosheets with electrochemically deposited MnO2-Pi are capable of yielding a synergistic effect in combination with high electrochemical performance and large surface area of MnO2-Pi. The reported electrochemical sensor exhibited a wide linear dynamic range (0.06–650 µM) and a low-level detection limit of 0.021 µM. An increase in the anodic peak current confirms the rapid transfer of electrons transfer arising between the Ti3C2Tx MXene and MnO2-Pi. The results attained substantiate that the fabricated sensor has enhanced selectivity, reproducibility, and stability toward the electrochemical determination of Vitamin B6 in real samples.

Modified electrochemical aptasensor for ultrasensitive detection of tetracycline: In silico and in vitro studies.

An ultrasensitive electrochemical aptasensor based on a glassy carbon electrode, modified by carbon nanofibers and carboxylated multi-walled carbon nanotubes was fabricated to detect tetracycline in food samples. The affinity of antibiotics, including kanamycin, tetracycline, ampicillin, and sulfadimethoxine toward desired sequences of aptamers and the stability of antibiotic-aptamer complexes were studied using molecular docking and molecular dynamic simulations. Moreover, the highest affinity and most stable complex were observed for tetracycline in complex with kanamycin-specific aptamer (KAP). Finally, KAP was used to develop an aptasensor. The central composite design (CCD) was used to optimize effective parameters. The biosensor achieved a wide dynamic linear range (1.0×10-17-1.0×10-5M) and a low limit of detection (2.28×10-18M) under optimized conditions using differential pulse voltammetry. Using the developed aptasensor, tetracycline residues in milk samples were determined.

Electrooxidation of Toxic Sulfite Material Using Ni-Ru-Based Heterometallo Supramolecular Polymer as Electrocatalyst: Synthesis and Kinetics Study

Considering the adverse effect of sulfite (SO3 2−), an effective Ni(II)- and Ru(II)-based heterometallic-supramolecular polymer (HMSMP) (polyNiRu) has been synthesized. PolyNiRu was characterized by Field-emission scanning electron microscopy (FE-SEM), and Fourier transmission infrared (FT-IR) spectroscopy. The formation of HMSMP was confirmed via UV–Vis spectroscopy. The molecular weight of polyNiRu (4.77 × 105 Da) was measured through intrinsic viscosity measurement following Mark-Houwink equation. The electrochemical behavior of polyNiRu modified glassy carbon electrode (polyNiRu_GCE) was investigated via CV and DPV. Furthermore, we have investigated the Tafel plot for this heterogeneous electrochemical system to calculate the number of transferred electrons during redox reactions. The limit of detection was found as 0.25 μM with a wide linear dynamic range of 10 to 600 μM. A probable surface mechanism has been studied toward SO3 2− oxidation at the interface of polyNiRu_GCE. Using the Butler-Volmer equation, the heterogeneous kinetic rate transfer constant and charge transfer coefficient were found as 1.02 × 10−6 cm2 s−1 and 0.68 respectively. These obtained parameters were further evaluated by simulated CV, which agreed with the experimental value. Excellent recovery with lower relative standard deviation (RSD) and high stability for 4000 s in analytic solution confirmed the reliability of using this polyNiRu_GCE in the practical assessment.

A highly sensitive and green electroanalytical method for the determination of favipiravir in pharmaceutical and biological fluids

BackgroundFavipiravir is currently used for the treatment of coronavirus disease-2019 (COVID-19).ObjectiveA highly sensitive and eco-friendly electroanalytical method was developed to quantify favipiravir.MethodThe voltammetric method optimized a sensor composed of reduced graphene oxide / modified carbon paste electrode in the presence of an anionic surfactant, improving the favipiravir detection limit. The investigation reveals that favipiravir-oxidation is a diffusion-controlled irreversible process. The effects of various pH and scan rates on oxidation anodic peak current were investigated.ResultsThe developed method offers a wide linear dynamic range of 1.5–420 ng/mL alongside a higher sensitivity with a limit of detection in the nanogram range (0.44 ng/mL) and a limit of quantification in the low nanogram range (1.34 ng/mL).ConclusionThe proposed method was applied for the determination of favipiravir in the dosage form, human plasma and urine samples. The developed method exhibited good selectivity in the presence of two potential electroactive biological interferants, uric acid which increases during favipiravir therapy and the recommended co-administered vitamin C. The organic solvent-free method greenness was evaluated via the Green Analytical Procedure Index, The present work offers a simple, sensitive and environment-friendly method fulfilling green chemistry concepts.

Modified electrochemical sensor via supramolecular structural functionalized graphene oxide for ultra-sensitive detection of gallic acid

Gallic acid (GA) is a synthetic polyphenolic compound that has been increasing interest due to its diverse biological activities, including anti-inflammatory, antioxidant, anti-tumor, scavenging free radicals, protecting cardiovascular diseases, and hypertension-lowering properties. The precise and rapid determination of GA content holds significant importance for human health. In this study, we present a cost-effective and highly sensitive electrochemical sensor employing a nanocomposite material, diester calix[4]arene functionalized graphene oxide (DEC4/GO) for the ultrasensitive detection of GA. The characterization of the as-synthesized nanocomposite material was carried out using various techniques, such as Fourier-Transform infrared (FT-IR), Raman spectroscopy, X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Tunneling Electron Microscopy (TEM), to ascertain its chemical composition, crystalline nature, phase purity, and structural morphology. The uniform deposition of DEC4/GO on the surface of a bare glass carbon electrode (GCE) was achieved via a drop casting method. In addition, the developed sensor DEC4/GO/GCE exhibits exceptional electrochemical response towards GA under optimized conditions, such as pH -7 phosphate-buffered saline (PBS) as a supporting electrolyte, a scan rate of 110 mV/s, and an applied potential window between −0.2 V and 0.8 V. The as-developed sensor demonstrated a wide linear dynamic range of 10–100 μM, resulting a brilliant linear calibration obtained for GA. Furthermore, the limit of detection (LOD) and quantification (LOQ) of the developed sensor were calculated as 0.01 and 0.03 μM respectively, lower than those reported for the other GA sensors. To validate the feasibility of our developed method, we analyzed the GA content in wine and green tea samples, achieving good recovery results. Overall, this study presents a promising electrochemical sensor platform for ultrasensitive detection of GA holding potential implications for various applications in health monitoring and food analysis.

A Novel Electrochemical Sensing Platform Based on Bimetallic Ru-Cu-MOF for the Voltammetric Detection of Ciprofloxacin Antibiotic

Metal-organic frameworks (MOFs) are an attractive class of highly ordered, crystalline, porous materials that exhibit large specific surface area, porosity, tunable structure and ease of functionalization. The presence of a number of uniformly dispersed metal components i.e. catalytic molecular units throughout the framework make MOF based materials a potential candidate for electrochemical sensing studies. However, pristine MOFs have the inherent drawbacks such as the inferior electrical conductivity that need to be addressed for its direct application in sensing platforms. In this context, the design of redox-active and highly conducting MOF is a research hotspot in the material science since it can overcome the inferior electrocatalytic activity of chemically modified electrodes (CME) based on pristine MOF. The integration of highly conducting metals into the framework is an efficient method to enhance the electric conductivity and thereby the electrochemical activity of synthesized material. The synergistic effect arising from the combination of different metal ions changes the surface electronic structure of MOF and thereby improve the mobility of charge carriers.Herein, an electrochemical sensing platform based on ruthenium doped Cu-MOF was developed for the sensitive detection of ciprofloxacin antibiotic. This work focuses on the synthetic strategy of Ru-Cu-TMA where the parent MOF, Cu-TMA, was synthesised by a facile room temperature mixing at ambient pressure. The present synthetic method is found to be a simple and efficient method compared to the conventional solvothermal method reported commonly for MOF synthesis. The successful integration of ruthenium into Cu-MOF created a number of electrocatalytic active sites which can favour the interaction with analyte species in sensing studies. The structural features and morphology of the synthesized MOF materials were studied using different characterization techniques like XRD, IR, SEM, XPS etc. The porous structure of MOF combined with higher reaction kinetics due to the incorporation of ruthenium cause a synergistic effect which makes the mixed-valent MOF a promising candidate for sensing studies. The composite, Ru-Cu-TMA, prepared was used as an electrode modifier for the sensitive detection of ciprofloxacin by electrochemical technique. Initially, the electrochemical activity of the chemically modified electrodes were examined and Ru-Cu-TMA modified electrode shows the higher current and fast electron transfer which paves the way for its application as sensing material. In addition, more number of active sites formed in MOF by ruthenium doping considerably increases the sensing performance of Ru-Cu-TMA. The electrochemical oxidation of ciprofloxacin on electrode surface is confirmed as an irreversible, diffusion-controlled process. The sensor exhibited a wide linear dynamic range (2.5 – 100 µM) with a lower limit of detection (3.29 nM) and sensitivity 0.0524 µA/µM. Moreover, the sensor demonstrates excellent selectivity, adequate stability, repeatability and can be used for real sample analysis.The porous structure of MOF combined with the enhanced reaction kinetics due to ruthenium doping together increased the electrochemical activity of the developed sensor. The enhanced electrochemical surface area and the increased number of active sites generated with the doping of ruthenium facilitates electron transfer with the electrode surface. Further, the aromatic ring system of CIP can interact with the conjugated ᴨ-electrons in MOF through stacking which further makes the Ru-Cu-TMA modified electrode a promising sensing platform. Figure 1

High sensitive detection of methamphetamine by high-performance aptasensing platform based on nickel oxide nanoparticles anchored on mxene

The concerns about the everyday abuse of narcotic materials, as a great alarm for society, have boosted many demands for sensitive and selective tracing of opiates in human biofluids. Herein, by taking advantage of nickel oxide nanoparticles (NiONPs) and MXene (NiONPs/MXene), an efficient sensing platform has been synthesized. The NiONPs/MXene nanocomposite increased the surface area and embedded many sites to load more aptamer (Apt) molecules as the bioreceptors of methamphetamine (MAMP) on the surface in the providing of the high-performance aptasensor. MAMP was measured by the aptasensor under a wide linear dynamic range from 1 pM to 50 mM with a very low limit of detection (LOD) of 333.3 fM within 40 min by consuming very small quantities of samples (10 µL) for each analysis. The highly selective and sensitive aptasensor was able to satisfactory measure MAMP in human serum, saliva and urine samples. The good repeatability and stability of the aptasensor revealed that the applied strategy may be a promising alternative for MAMP assay in the biofluids and street samples that is highly required as a non-invasive method for legal and clinical organizations.

A core-molecule-shell Au@PATP@Ag nanorod for nicotine detection based on surface-enhanced Raman scattering technology

Nicotine is an addictive substance often found in tobacco and cigarette smoke and excessive exposure to it can cause various diseases. Herein, core-molecule-shell gold/4-aminothiophenol/silver nanorods (Au@PATP@Ag NRs) were prepared for quantitative detection of nicotine by using surface-enhanced Raman scattering (SERS) technology. The obtained Au@PATP@Ag NRs showed an outstanding SERS effect due to the plasticity of their morphology and the bimetallic synergistic effect between the excellent stability of Au and the highly enhanced effect of Ag. The Au@PATP@Ag NRs substrate exhibited an extremely high enhancement factor (EF) of 2.17 × 107. In addition, in-situ synthesized PATP was used as an internal standard to correct signal fluctuation and improve the reliability of quantitative nicotine detection. A wide linear dynamic range from 10−8 to 10−3 M was obtained and an ultra-low limit of detection (LOD) was about 3.12 × 10−9 M, which was superior to most of previously reported methods. This work has also been used for determining nicotine content in cigarettes and simulated environmental tobacco smoke by using a portable device. These results indicated that the developed SERS method had many potential applications in the quantitative determination of nicotine in real tobacco samples.

A green compliant hand-held selective electrode device for monitoring active pharmaceuticals and the kinetics of their degradation

An in-line smartphone connected to a screen-printed selective electrode hand-held device was used to determine the concentration of distigmine bromide (DB) in its pure and dosage forms as well as its degradation kinetics by continuously measuring the change in the produced emf over time. The main objective, supported by the data presented, is to produce a highly reliable smartphone integrated selective sensor as a portable analyzer with potential high cloud connectivity combining a wide linear dynamic range, the fastest response time with the lowest limits of detection and quantitation while best integrating green analytical chemistry principles. The choice of ionophore used in this approach was guided by computation and the data obtained was compared with traditional analytical techniques. DB, for which there are no previously reported stability-indicating methods and for which four novel such methods are proposed here, was selected as a model drug for this work. At-line UV-spectrophotometry DB assay was obtained by measuring the difference between the spectra of the degradation product and the same concentration of intact drug. The degradation kinetics were studied by this method through tracking the decrease of DB absorbance and/or the increase of a generated degradation product signal over time. Off-line separation based HPLC and TLC stability-indicating methods for DB were also presented. All methods employed in this work were validated for accuracy, precision, specificity, repeatability, linearity, range, detection and quantification limits according to the ICH guidelines and were applied to the analysis of laboratory prepared mixtures as well as commercial products. While all methods proposed were shown to be highly reliable, the smartphone integrated selective sensor is highlighted as a portable analyzer with potential high cloud connectivity and was shown to combine a wide linear dynamic range, the fastest response time with the lowest limits of detection and quantitation while best integrating green analytical chemistry principles.

Recent Advances in Electrochemical Sensors for Sulfur-Containing Antioxidants.

Sulfur-containing antioxidants are an important part of the antioxidant defense systems in living organisms under the frame of a thiol-disulfide equilibrium. Among them, l-cysteine, l-homocysteine, l-methionine, glutathione, and α-lipoic acid are the most typical representatives. Their actions in living systems are briefly discussed. Being electroactive, sulfur-containing antioxidants are interesting analytes to be determined using various types of electrochemical sensors. Attention is paid to the chemically modified electrodes with various nanostructured coverages. The analytical capabilities of electrochemical sensors for sulfur-containing antioxidant quantification are summarized and discussed. The data are summarized and presented on the basis of the electrode surface modifier applied, i.e., carbon nanomaterials, metal and metal oxide nanoparticles (NPs) and nanostructures, organic mediators, polymeric coverage, and mixed modifiers. The combination of various types of nanomaterials provides a wider linear dynamic range, lower limits of detection, and higher selectivity in comparison to bare electrodes and sensors based on the one type of surface modifier. The perspective of the combination of chromatography with electrochemical detection providing the possibility for simultaneous determination of sulfur-containing antioxidants in a complex matrix has also been discussed.