Design and optimization of a cost-effective paper-based voltammetric sensor for the determination of trinitrotoluene (TNT) utilizing cysteamine-linked Fe3O4 @Au nanocomposite.

This paper presents the development and optimization of a cost-effective paper electrochemical sensor for the detection of TNT using Fe3O4-Au core-shell nanoparticles modified with cysteamine (Fe3O4@Au/CA). The sensor was constructed by modifying a graphite paste with the aforementioned nanoparticles, which facilitated the formation of a Meisenheimer complex between cysteamine and TNT as an electron donor and an electron acceptor, respectively. The central composite design was employed to optimize four key parameters pH, modifier percentage, contact time, and buffer type to enhance the performance of the sensor. The detection limit was found to be 0.5 nM of TNT, while the linear range of the electrode response spanned from 0.002 µM to 10 µM. The simplicity and low cost of the sensor make it highly attractive for practical applications, particularly in scenarios where rapid and on-site TNT detection is required.

Aerosol assisted synthesis of a pH responsive curcumin anticancer drug nanocarrier using chitosan and alginate natural polymers.

In recent years, several nanocarrier synthesis methods have been developed. In cancer therapy, the use of smart nanocarriers is of interest. Smart nanocarriers respond to their environment and can release their cargo in a controlled manner under the action of internal or external stimuli. In this work, we report on the development of an aerosol-assisted method for the synthesis of curcumin-loaded chitosan/alginate-based polymeric nanocarrier (CurNCs). A custom-fabricated multi-nebulizer system was utilized for the synthesis of CurNCs. The developed system comprises three main parts a sprayer, an electric heater tunnel, and a collector. Curcumin and chitosan solutions were sprayed using a pneumatic multinebulizer into the electric heater tunnel to form chitosan-curcumin assemblies. Then, the aerosol was guided into the collector solution containing sodium alginate and tri-poly phosphate aqueous solution for further cross-linkage. The synthesized CurNCs were characterized using TEM, DLS, and FTIR techniques. The TEM size of the nanoparticles was 8.62 ± 2.25 nm. The release experiments revealed that the nanocarrier is sensitive to the environment pH as more curcumin is released at acidic pH values (as is the case for cancerous tissues) compared to physiological pH. The curcumin content of the nanocarrier was 77.27 mg g-1 with a drug loading efficiency of 62%. The in-vitro cytotoxicity of the synthesized nanocarrier was evaluated against the MCF7 breast cancer cell line. The IC50 concentrations for CurNCs and curcumin were obtained as 14.86 and 16.45 mg mL-1, respectively. The results showed that while the empty nanocarrier shows non-significant cytotoxicity, the CurNCs impact the cell culture and cause prolonged cell deaths. Overall, pH-responsive curcumin polymeric nanocarrier was synthesized using a custom fabricated aerosol-based method. The method enabled fast and feasible synthesis of the nanocarrier with high efficiency.

Fabrication of impedimetric sensor based on metallic nanoparticle for the determination of mesna anticancer drug.

Electrochemical impedance spectroscopy (EIS) is a highly effective technique for studying the surface of electrodes in great detail. EIS-based electrochemical sensors have been widely reported, which measure the charge transfer resistance (Rct) of redox probes on electrode surfaces to monitor the binding of target molecules. One of the protective drugs against hemorrhagic cystitis caused by oxazaphosphorine chemotherapy drugs such as ifosfamide, cyclophosphamide and trophosphamide is Mesna (sodium salt of 2-mercaptoethanesulfonate). The increase in the use of Mesna due to the high consumption of anti-cancer drugs, the determination of this drug in biological samples is of particular importance. So far, no electrochemical method has been reported to measure Mesna. In this research, a novel impedimetric sensor based on a glassy carbon electrode (GCE) modified with oxidized multiwalled carbon nanotubes (MWCNTs)/gold nanoparticle (AuNPs) (denoted as Au NPs/MWCNTs/GCE) for impedimetric determination of Mesna anticancer drug was developed. The modified electrode materials were characterized by field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX), and EIS. The electrochemical behavior of Mesna at the surface of Au NPs/MWCNTs/GCE was studied by an impedimetric method. The detection mechanism of Mesna using the proposed impedimetric sensor relied on the increase in the Rct value of [Fe (CN)6]3-/4- as an electrochemical probe in the presence of Mesna compared to the absence of Mesna as the analyte. Under the optimum condition, which covered two linear dynamic ranges from 0.06 nmol L-1 to 1.0 nmol L-1 and 1.0 nmol L-1 to 130.0 µmol L-1, respectively. The detection limit was 0.02 nmol L-1. Finally, the performance of the proposed sensor was investigated for Mesna electrochemical detection in biological samples.

A paired emitter-detector diode-based photometer for the determination of sodium hypochlorite adulteration in milk.

This paper reports on developing a low cost but efficient paired emitter-detector diode (PEDD)-based photometer. The photometer consists of a white light-emitting diode (LED) as the emitter diode, an RGB LED as the detector diode, and a multimeter for recoding the signal. The developed PEDD-based photometer was utilized for the determination of liquid bleach adulteration in cow milk samples. N,N-Diethyl-p-phenylenediamine sulfate aqueous solution of pH 6 was used as a probe to monitor the presence of residual active chlorine in milk. The results showed that the developed method could be used to determine sodium hypochlorite in the concentration range of 0.5 to 20.0 ppm Cl2 with 0.14 and 0.46 ppm Cl2 limit of detection and limit of quantification, respectively. The intraday and interday precisions of the method at two concentration levels of 5.5 and 13.7 ppm Cl2 were 1.04% and 0.52%, and 1.81% and 1.02%, respectively. The recoveries of 114.2% and 106.9% were obtained for 5.5 and 13.7 ppm Cl2 concentrations levels, respectively. Real sample analyzes results showed that "maybe" liquid bleach adulteration in milk is the case for local distributors of raw milk.

Transdermal Delivery of Insulin Using Combination of Iontophoresis and Deep Eutectic Solvents as Chemical Penetration Enhancers: In Vitro and in Vivo Evaluations.

A serious challenge in transdermal iontophoresis (IP) delivery of insulin (INS) is the low permeability of the drug across the skin. In this paper, we introduced deep eutectic solvent (DESs) as novel chemical penetration enhancers (CPEs) for transdermal IP of INS across rat skin, both in vitro and in vivo. Three different DESs based on choline chloride (ChCl), namely, ChCl/UR (ChCl and urea), ChCl/GLY (ChCl and glycerol), and ChCl/EG (ChCl and ethylene glycol) in the 1:2 molar ratios have been prepared. To evaluate the capability of studied DESs as CPEs for IP delivery of INS, the rat skin sample was treated with each DES. The effects of different experimental parameters (current density, formulation pH, INS concentration, NaCl concentration, and treatment time) on the in vitro transdermal iontophoretic delivery of INS were investigated. The in vitro permeation studies exhibited that INS was easily delivered employing ChCl/EG, and ChCl/GLY treatments, compared with ChCl/UR: the cumulative amount of permeated INS at the end of the experiment (Q24h) was found to be 131.0, 89.4, and 29.6 µg cm-2 in the presence of ChCl/EG, ChCl/GLY, and ChCl/UR, respectively. The differences in Q24h values of INS are due to the different capabilities of the studied DESs to treat the epidermis layer of skin. In vivo experiments revealed that the blood glucose level in diabetic rats could be decreased using ChCl/EG, and ChCl/GLY as novel CPEs in the IP delivery of INS. The presented work will open new doors towards searching for novel CPEs in the development of transdermal IP of INS.

Sensitive and selective impedimetric determination of TNT using RSM-CCD optimization.

Detection of trace amounts of 2,4,6-Trinitrotoluene as a widely used explosive in the military and industrial sectors is of vital importance due to security and environmental concerns. The sensitive and selective measurement characteristics of the compound still is considered a challenge for analytical chemists. Unlike conventional optical and electrochemical methods, the electrochemical impedance spectroscopy technique (EIS), has a very high sensitivity, but it faces a significant challenge in that it requires complex and expensive steps to modify the electrode surface with selective agents. We reported the design and construction of an inexpensive, simple, sensitive, and selective impedimetric electrochemical TNT sensor based on the formation of a Meisenheimer complex between magnetic multiwalled carbon nanotubes modified with aminopropyl triethoxysilane (MMWCNTs @ APTES) and TNT. The formation of the mentioned charge transfer complex at the electrode-solution interface blocks the electrode surface and disrupts the charge transfer in [(Fe (CN) 6)] 3-/4- redox probe system. Charge transfer resistance changes (ΔRCT) were used as an analytical response that corresponded to TNT concentration. To investigate the influence of effective parameters on the electrode response, such as pH, contact time, and modifier percentage, the response surface methodology based on central composite design (RSM-CCD) was used. The calibration curve was achieved in the range of 1-500 nM with a detection limit of 0.15 nM under optimal conditions, which included pH of 8.29, contact time of 479 s, and modifier percentage of 12.38% (w/w). The selectivity of the constructed electrode towards several nitroaromatic species was investigated, and no significant interference was found. Finally, the proposed sensor was able to successfully measure TNT in various water samples with satisfactory recovery percentages.

Rapid determination of ampyra in urine samples using dispersive liquid-liquid microextraction coupled with ion mobility spectrometry.

Ampyra (AMP, 4-Aminopyridine) is a potassium channel blocker that attracts growing research interest due to its adverse effects at high doses. The fast analysis of AMP is challenging because it typically requires complex analytical techniques. In this research, we developed and validated a novel method to assess the fast and quantitative analysis of AMP from real samples. This method combines the strength of ion mobility spectrometry (IMS) for rapid detection and the dispersive liquid-liquid microextraction as a fast and effective preconcentration method for the preconcentration/extraction of AMP. In this method, Ag nanoparticles were used as modifier agents. Moreover, the proposed mechanism for interaction of AMP with AgNPs was investigated based on the quantum theory of atoms in molecules (QTAIM) analysis. Also, the sensitivity of the proposed method was improved through the application of a delay on the carrier gas flow after sample injection. Under the optimum conditions, the developed method detected AMP in the linear range of 0.4-16 µmol L-1 with a detection limit of 0.12 µmol L-1. Finally, the developed method was successfully employed to quantify AMP in urine samples. Method validation was performed by comparing our results with those obtained by HPLC-UV/Vis, confirming the applicability of the proposed method for the AMP analysis in real samples. The proposed method will open up a new door toward developing simple, fast, and effective analytical methods.

Simultaneous determination of Pb2+ and Hg2+ at food specimens by a Melamine-based covalent organic framework modified glassy carbon electrode.

Heavy metals determination is of great importance. In this respect, a recently synthesized melamine-based covalent organic framework (Schiff base network1 (SNW1)) was used in this research as a novel modifier to alter a glassy carbon electrode for the simultaneous anodic stripping square wave voltammetric measurement of Pb2+ and Hg2+ ions. At first, the complexation of SNW1 with Pb2+ and Hg2+ ions were evaluated by density functional theory calculations. Afterward, the modified electrode was characterized by various techniques including Fourier-transform infrared spectroscopy, Scanning electron microscopy, energy dispersive X-ray analysis, cyclic voltammetry, and electrochemical impedance spectroscopy. Then, all of the effective experimental factors including pH, supporting electrolyte type, and instrumental parameters were optimized. Under optimized conditions (pH = 2.0, deposition time = 150 S, accumulation potential = -1000 (mV), pulse amplitude = 40 mV, frequency = 50 Hz, and voltage step = 7 mV) the designed sensor showed a linear response over the concentration ranges of 0.01-0.3 and 0.05-0.3 µmol/L for Pb2+ and Hg2+ respectively with a detection limit of 0.00072 and 0.01211 µmol/L. In the end, the designed electrochemical sensor was successfully employed for simultaneous measurement of Pb2+ and Hg2+ at different edible samples.

Utilizing inner filter effect in resonance Rayleigh scattering technique: a case study with silver nanocubes as RRS probe and several analytes as absorbers.

It was demonstrated that the mechanism of the inner filter effect (IFE) can emerge well in the resonance Rayleigh scattering (RRS) technique and be utilized as a new analytical method in the design of innovative IFE-based sensors. To prove this process, silver nanocubes (Ag NCs) with tunable extinction spectra were selected as RRS probes, and three analytes, doxorubicin (DOX), sunitinib (SUN), and Alizarin Red S (ARS), were considered as the typical absorbers. In addition, in the presence of SUN as a typical analyte, the quenching of the RRS signal of Ag NCs, with λmax of 419 nm, was linear in the range 0.01 to 2.5 µM of SUN. The limit of detection (LOD) was 0.0025 µM. The introduced method was then used to develop a dual-signal assay for the ratiometric determination of Al3+ ions. The suggested dual-signal assay was based on the color changes of ARS caused by Al3+ and the IFE between ARS and Ag NCs. The obtained results showed that the two characteristics of response sensitivity and linear dynamic range are very satisfactory for sensing Al3+ ions. The findings of this study demonstrate that the newly developed IFE mechanism can be employed as an attractive and highly efficient analytical technique for measuring different analytes.

Effect of light at different wavelengths on polyol synthesis of silver nanocubes.

Despite the presence of light-sensitive species in the polyol synthesis of silver nanocubes, the influence of light on it has yet to be investigated. Herein, we demonstrated that light radiation, by generating plasmon-based hot electrons and subsequently increasing the reduction rate of Ag+ in the system, in addition to enhancing the growth rate of nanocubes, causes twinned seeds, which these seeds are then converted into nanorods and right bipyramids. With shorter, higher energy wavelengths, Ag+ reduction progresses more quickly, resulting in structures with more twin planes. The overlap of the excitation wavelength and the band gap of Ag2S clusters formed in the early stages of synthesis accelerates the rate of reaction at low-energy excitation. According to our findings, the surfactant polyvinylpyrrolidone acts as a photochemical relay to drive the growth of silver nanoparticles. Overall, this work emphasizes the impact of excitation light on polyol synthesis as a technique for generating Ag nanocubes of various sizes.

Ultra-trace levels voltammetric determination of Pb2+ in the presence of Bi3+ at food samples by a Fe3O4@Schiff base Network1 modified glassy carbon electrode.

In this research, a highly sensitive electrochemical sensor was developed for the square wave anodic stripping voltammetric determination of Pb2+ at ultra-trace levels. A Glassy carbon electrode was modified with an in-situ electroplated bismuth film and the nanocomposite of a recently synthesized melamine based covalent organic framework (schiff base network1 (SNW1)) and Fe3O4 nanoparticles (Fe3O4@SNW1). The obtained results exhibit clearly that combination of Fe3O4@SNW1 and in-situ electroplated bismuth film enhances the sensitivity of the modified electrode towards Pb2+ remarkably. A Plackett-Burman design was implemented for screening experimental factors to specify the significant variables influencing the sensitivity of the electroanalytical method. Afterward, the effective factors were optimized using Box-Behnken design (BBD). Under optimized conditions, the proposed electrode showed a linear response towards Pb2+ in the concentration range of 0.003-0.3 µmol L-1 with the detection limit of 0.95 nmol L-1. The selectivity of the fabricated electrode towards different ionic species were checked out and no serious interference was observed. At the end, the application of the designed sensor in the determination of Pb2+ at 10 different edible specimens were investigated and the obtained recovery values were in the range of (95.56-106.64%) indicating the successful performance of the designed sensor.

QSAR analysis on a large and diverse set of potent phosphoinositide 3-kinase gamma (PI3Kγ) inhibitors using MLR and ANN methods.

Phosphorylation of PI3Kγ as a member of lipid kinases-enzymes, plays a crucial role in regulating immune cells through the generation of intracellular signals. Deregulation of this pathway is involved in several tumors. In this research, diverse sets of potent and selective isoform-specific PI3Kγ inhibitors whose drug-likeness was confirmed based on Lipinski's rule of five were used in the modeling process. Genetic algorithm (GA)-based multivariate analysis was employed on the half-maximal inhibitory concentration (IC50) of them. In this way, multiple linear regression (MLR) and artificial neural network (ANN) algorithm, were used to QSAR models construction on 245 compounds with a wide range of pIC50 (5.23-9.32). The stability and robustness of the models have been evaluated by external and internal validation methods (R2 0.623-0.642, RMSE 0.464-0.473, F 40.114, Q2LOO 0.600, and R2y-random 0.011). External verification using a wide variety of structures out of the training and test sets show that ANN is superior to MLR. The descriptors entered into the model are in good agreement with the X-ray structures of target-ligand complexes; so the model is interpretable. Finally, Williams plot-based analysis was applied to simultaneously compare the inhibitory activity and structural similarity of training, test and validation sets.

Application of Fe3O4@TbBd nanobeads in microextraction by packed sorbent (MEPS) for determination of BTEXs biomarkers by HPLC-UV in urine samples.

A relatively new adsorbent based on covalent organic frameworks (COFs) was employed for the first time to extract and determine Trans, trans-muconic acid (tt-MA), Mandelic acid (MA), Hippuric acid (HA), and 3-Methylhippuric acid (m-MHA) in urine. For this purpose, microextraction was performed using the packed sorbent (MEPS) method. Following the extraction process, the prepared samples were specified via the high-performance liquid chromatography-ultraviolet detector system. The precipitation polymerization was applied to synthesize the Fe3O4@TbBd nanobeads, and the morphological and dimensional structures of the products were specified with FE-SEM images. Some key variables affecting the extraction efficiency (i.e., sample volume, elution volume, condition and washing solvents, type and volume of elution solvent, extraction cycles, temperature, and pH of the sample solution) were investigated. In ideal conditions, the limit of detection (LOD) was obtained from 0.02 µg/ml for tt-MA to 0.5 µg/ml for MA. Calibration curves (at five-point) were plotted in the range 0.05-5 µg/ml for tt-MA to 1-300 µg/ml for MA (R2 > 0.98). Moreover, intra- and inter-day precision values were 3.1-5.5 and 4.6-9.8%, respectively. The developed method was successfully employed to determine four analytes in three concentrations (low, medium, and high QCs). The results showed a satisfactory recovery (70-87%). COF-MEPS technique is a rapid, easy, user-friendly, and environment-friendly method for separating the minimum values of all BTEXs chief biomarkers from urine samples without using complicated processes and only with one adsorbent. Also, it can be a good alternative for biomonitoring the workers exposed to BTEX compounds in occupational and environmental access.

Simultaneous determination of BoNT/A and /E using an electrochemical sandwich immunoassay based on the nanomagnetic immunosensing platform.

Developing new ultrasensitive assays for the detection of the presence, and determination of the serotype of the most poisonous material known i.e. botulinum neurotoxin (BoNT) is vital to human health and the wellbeing of the surrounding environment. Here, an electrochemical sandwich immunoassay with high sensitivity is adopted to achieve simultaneous determination of BoNT serotypes A and E based on polystyrene@polydopamine/Cd2+ and Ag nanoparticles acting as monoclonal antibody labels. Two well-separated peaks with strong electrochemical signals are generated by the labels, allowing for the simultaneous detection of two analytes existing on the electrode. To obtain well-oriented polyclonal antibodies immobilization, boronic acid is directly attached to the magnetic core/metal-organic framework (MOF) shell nanoagent surfaces without the requirement of a long and flexible spacer. Accordingly, it is possible to directly detect the metal ion labels through square wave voltammetry without the metal pre-concentration step. This results in distinct and well-defined voltammetric peaks, pertaining to each sandwich-type immunocomplexes. The limits of detection of BoNT/A and BoNT/E analyses were found to be 0.04 and 0.16 pg mL-1 with the linear dynamic ranges of 0.1-1000 and 0.5-1000 pg mL-1, respectively. Based on the obtained results, this immunosensor has the wide linear ranges, while also exhibiting low limits of detection along with good stability and reproducibility.

PVP-coated silver nanocubes as RRS probe for sensitive determination of Haloperidol in real samples.

Polyol synthesis of silver nanocubes (Ag NCs) under dark conditions yielded nanoparticles with high uniformity and purity, as well as edge lengths of 42 nm with good stability and scattering cross-section. These nanoparticles were characterized by SEM, TEM, and Uv-vis spectroscopy. The presence of polyvinylpyrrolidone (PVP) as a capping agent on the surface of Ag NCs, as well as its satisfactory interaction level with Haloperidol (Hp) as an antipsychotic drug, has led to the use of these nanoparticles as Resonance RayleighScattering (RRS) probe to measure Hp. Indeed, Hp resulted in reducing the RRS signal of Ag NCs, and this change in RRS intensity was linear in the range of 10.0 to 800.0 µg L-1 of Hp. The limits of detection (LOD) and quantification (LOQ) were found to be 1.5 and 5.0 µg L-1, respectively. The influence of interfering species was studied, and it was found that the suggested method has good selectivity and can be used to monitor Hp in actual samples. As a result, this RRS probe operated well in determining Hp in pharmaceutical and human plasma samples with satisfactory recovery.

Wearable Potentiometric Sensor Based on Na0.44MnO2 for Non-invasive Monitoring of Sodium Ions in Sweat.

Here, we present a wearable potentiometric ion sensor for real-time monitoring of sodium ions (Na+) in human sweat samples using Na0.44MnO2 as the sensing material. Na0.44MnO2 is an attractive material for developing wearable electrochemical sensors due to its good Na+ incorporation ability, electrical conductivity, stability, and low fabrication cost. In the first step, the analytical performance of the electrode prepared using Na0.44MnO2 is presented. Then, a miniaturized potentiometric cell integrated into a wearable substrate is developed, which reveals a Nernstian response (58 mV dec-1). We achieved the detection of Na+ in the linear ranges of 0.21-24.54 mmol L-1, which is well within the physiological range of Na+. Finally, for on-body sweat analysis, the potentiometric sensor is fully integrated into a headband textile. This platform can be employed for non-invasive analysis of Na+ in human sweat for healthcare and disease diagnosis.

Controlled Transdermal Iontophoresis of Insulin from Water-Soluble Polypyrrole Nanoparticles: An In Vitro Study.

The iontophoresis delivery of insulin (INS) remains a serious challenge due to the low permeability of the drug through the skin. This work aims to investigate the potential of water-soluble polypyrrole nanoparticles (WS-PPyNPs) as a drug donor matrix for controlled transdermal iontophoresis of INS. WS-PPyNPs have been prepared via a simple chemical polymerization in the presence of sodium dodecyl sulfate (SDS) as both dopant and the stabilizing agent. The synthesis of the soluble polymer was characterized using field emission scanning electron microscopy (FESEM), dynamic light scattering (DLS), fluorescence spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy. The loading mechanism of INS onto the WS-PPyNPs is based on the fact that the drug molecules can be replaced with doped dodecyl sulfate. A two-compartment Franz-type diffusion cell was employed to study the effect of current density, formulation pH, INS concentration, and sodium chloride concentration on anodal iontophoresis (AIP) and cathodal iontophoresis (CIP) of INS across the rat skin. Both AIP and CIP delivery of INS using WS-PPyNPs were significantly increased compared to passive delivery. Furthermore, while the AIP experiment (60 min at 0.13 mA cm-2) show low cumulative drug permeation for INS (about 20.48 µg cm-2); the CIP stimulation exhibited a cumulative drug permeation of 68.29 µg cm-2. This improvement is due to the separation of positively charged WS-PPyNPs and negatively charged INS that has occurred in the presence of cathodal stimulation. The obtained results confirm the potential applicability of WS-PPyNPs as an effective approach in the development of controlled transdermal iontophoresis of INS.

Crystal violet-modified HKUST-1 framework with improved hydrostability as an efficient adsorbent for direct solid-phase microextraction.

Metal-organic frameworks (MOFs) have received extensive attention in adsorption applications owing to their high surface area. However, some MOFs do not perform well as the extraction medium when used under aqueous conditions. The low hydrostability of MOFs limits the practical application of these materials in solid-phase microextraction (SPME). Here, the fabrication of a water resistance SPME fiber coating is introduced based on the crystal violet (CV)-modified HKUST-1 framework on copper (Cu@HKUST-1@CV). The HKUST-1 was prepared by the in situ growth method, followed by post-synthetic modification of HKUST-1 with the CV layer. The preparation of the modified HKUST-1 was characterized by FESEM, XRD, FTIR, and DFT approaches. The prepared SPME coating was successfully employed for the quantification of anthracene (AN), as a model analyte, in water samples. The limit of detection was 0.8 ng mL-1. The developed method will open up a new door towards searching for promising materials in SPME applications.

Target -responsive host-guest binding-driven dual-sensing readout for enhanced electrochemical chiral analysis.

Achieving efficient chiral discrimination by a convenient method remains a challenge in pharmaceutical and biotechnology industries. Our aim in this paper was to develop a dual-signaling enantioselective sensing strategy based on the competitive binding assay. A combination of ß-cyclodextrin (ß-CD) and methylene blue (MB) was used as an enantioselective discrimination probe to develop a straightforward electrochemical chiral sensor using the drug naproxen (R-and S-NaX) as the representative enantiomers. The principle relied on the difference between two enantiomers in the ability to replace a pre-binding redox probe, which in turn resulted in different dual signals for the two enantiomers. The applicability of the optimized procedure was demonstrated by the analysis of NaX enantiomers in the range of 0.4-6.0 µM. Featuring both signal-on and signal-off elements, the electrode presented significantly enhanced electrochemical activity with a low limit of detection (LOD) of 0.07 µM. We expect that our work will inspire interesting engineering strategies for developing novel enantioselective electrochemical sensors.

Electrochemical sandwich-type immunosensor for the detection of PSA based on a trimetallic AgAuPt nanocomposite synthesized using the galvanic replacement reaction.

A sandwich-type electrochemical immunoassay was introduced for the determination of the prostate-specific antigen (PSA) biomarker. A direct and simple galvanic replacement reaction was performed between the Ag framework and metallic salts of tetrachloroauric(iii) acid trihydrate and chloroplatinic acid to produce a trimetallic composite of AgAuPt. The trimetallic composite of AgAuPt was applied to the preparation of the capture layer of the immunoassay for stabilizing the primary Ab at the surface of the prepared composite. The immunoassay detection layer was also prepared using a labeled antibody containing a bimetallic composite of AgPt as a label. The various procedures in the immunoassay fabrication were monitored step by step using cyclic voltammetry and electrochemical impedance spectroscopy. Also, the electrochemical determination of PSA was performed using differential pulse voltammetry in the presence of the ferrocene redox probe and H2O2. Furthermore, the effective parameters in the fabrication of the immunoassay included the drop volume of the AgAuPt trimetallic composite and the incubation time for the immobilization of biomolecules (i.e., Ab1, BSA, PSA, and labeled Ab2), and the concentration of H2O2 were optimized during the determination of PSA. Then, the determination of PSA was performed under optimized conditions. It could be seen that there was a linear relation between the PSA concentration and DPV responses in the concentration range of 50 pg mL-1 to 500 ng mL-1 and the limit of detection (LOD) for the proposed immunoassay was calculated as 17.0 pg mL-1. In the following investigation, the cross-reactivity of the proposed immunoassay was studied in the presence of BSA, CEA, IgG, and human hepatitis surface antigen, in which the results showed a negligible change in the performance of the immunoassay.