Modification of electrodes with nanostructured functionalized thiadiazole polymer film and its application to the determination of ascorbic acid

Preparation of electrochemical sensor based on glassy carbon electrode and its specificity and sensitivity for directional detection of antibiotic resistance genes spreading in the water environment

Antibiotic-resistant bacteria/resistance genes (ARB/ARGs) have been paid much attention due to the environmental risks they might bring. They were demonstrated to be widespread in surface water and wastewater. Determining the concentrations of ARGs is the first step to evaluate the degree of pollution. In this study, electrochemical detection technology was studied due to its advantages of low cost, fast response, and satisfactory selectivity. Additionally, the electrochemical sensor technology was used to determine the concentration of a ubiquitous ARG (ampicillin gene bla_TEM) in the water environment. A kind of electrochemical sensor was prepared on a glassy carbon electrode (GCE). The results of X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV) curves indicated that the single-stranded DNA (ssDNA) probe can be successfully immobilized on the surface of the GCE. In addition, the performance of hybridization between the ssDNA probe and the target DNA at diverse temperatures was compared, of which 35 °C was the optimum. Moreover, the change of charge transfer resistance (ΔRct) for the GCE sensor hybridizing with complementary DNA was much higher than that of DNA with the mismatched base, which indicated that the electrochemical sensor prepared in this study was specific. The sensitivity of the sensor was also proved by the strong correlation between the concentrations of ARGs and ΔRct (with the correlation coefficient (R²) of 0.9905). All in all, this study is meaningful for the comprehend on the detection of ARGs through the electrochemical method.

Functionalized dual modification of covalent organic framework for efficient and rapid trace heavy metals removal from drinking water

A key challenge in trace heavy metals removal from drinking water by adsorption technology is to achieve high adsorption capacity and rapid uptake speed of adsorbent. Herein, we report a functionalized double modified covalent organic framework (DMTD-COF-SH) bearing high-density sulfur and nitrogen chelating groups provided simultaneously by 2,5-dimercapto-1,3,4-thiadiazole (DMTD) and 1,2-ethanedithiol, which was prepared via a facile one-pot thiol-ene "click" reaction. PXRD, FTIR, XPS, SEM, BET and ¹³C MAS NMR confirmed their successful graft, and DMTD was found to be more easily grafted on the COF surface layer than 1,2-ethanedithiol. The as-prepared DMTD-COF-SH showed remarkable adsorption capacity and ultrafast uptake dynamics to trace heavy metals owing to the synergistic effects resulting from densely populated sulfur and nitrogen chelating groups within ordered COF mesopores and at the COF surface. On the basis of the drinking water treatment units standard NSF/ANSI 53-2020, when the adsorbent dosage was 10 mg/30 mL and 20 mg L^-1 calcium ions coexisted, the lead concentration decreased from initial 150 μg L^-1 to 2.89 μg L^-1 within 10 s, far below the allowable limit of world health organization (WHO) drinking water standard (10 μg L^-1), and the maximum adsorption capacity meeting the standard attained 14.22 mg g^-1. The adsorbent also exhibited excellent stability, wide applicable pH range and outstanding adsorption performance for coexisting trace lead, mercury, cadmium, chromium (VI) and copper in tap water, indicating that the DMTD-COF-SH material has excellent application prospect for trace heavy metals removal from drinking water.

Fabrication of low-cost sustainable electrocatalyst: a diagnostic tool for multifunctional disorders in human fluids

In purine metabolism, the xanthine oxidoreductase enzyme converts hypoxanthine (HXN) to xanthine (XN) and XN to uric acid (UA). This leads to the deposition of UA crystals in several parts of the body and the serum UA level might be associated with various multifunctional disorders. The dietary intake of caffeine (CF) and ascorbic acid (AA) decreases the UA level in the serum, which leads to cellular damage. Hence, it is highly needed to monitor the UA level in the presence of AA, XN, HXN, and CF and vice versa. Considering this sequence of complications, the present paper reports the fabrication of an electrochemical sensor using low-cost N-doped carbon dots (CDs) for the selective and simultaneous determination of UA in the presence of AA, XN, HXN, and CF at the physiological pH. The colloidal solution of CDs was prepared by the pyrolysis of asparagine and fabricated on a GC electrode by cycling the potential from -0.20 to +1.2 V in a solution containing CDs and 0.01 M H2SO4. Here, the surface -NH2 functionalities of CDs were used to make a thin film of CDs on the GC electrode. FT-IR spectroscopy confirmed the involvement of the -NH2 group in the formation of the CD film. HR-TEM analysis depicts that the formed CDs showed spherical particles with a size of 1.67 nm and SEM analysis exhibits the 89 nm CD film on the GC electrode surface. The fabricated CD film was successfully used for the sensitive and selective determination of UA. The determination of UA was achieved selectively in a mixture consisting of AA, XN, HXN, and CF with 50-fold high concentration. The CDs-film fabricated electrode has several benefits over the bare electrode: (i) well-resolved oxidation peaks for five analytes, (ii) boosted sensitivity, (iii) shifted oxidation as well as on-set potentials toward less positive potentials, and (iv) high stability. The practical utility of the present sensor was tested by simultaneously determining the multifactorial disorders-causing agents in human fluids. The electrocatalyst developed in the present study is sustainable and can be used for multiple analyses; besides, the electrochemical method used for the fabrication of the CD film is environmentally benign.

An electrochemical sandwich-type aptasensor for determination of lipocalin-2 based on graphene oxide/polymer composite and gold nanoparticles

In this work, we reported an electrochemical aptasensor based on the poly-3-amino-1,2,4-triazole-5-thiol/graphene oxide composite (P(ATT)-GO) and gold nanoparticles (AuNPs) modified graphite screen-printed electrode (GSPE) (GSPE/P(ATT)-GO/AuNPs) for determination of lipocalin-2 (LCN2) (neutrophil gelatinase-associated lipocalin). A sandwich based strategy was utilized to enhance the electrochemical signal. First, a thiol tethered DNA aptamer was immobilized onto the composite electrode. Then, the LCN2 solution was incubated with the aptamer modified GSPE/P(ATT)-GO/AuNPs. Secondary aptamer (Apt2) peculiar to the LCN2 and labeled with biotin was interacted with the LCN2. A streptavidin-alkaline phosphatase conjugate was then applied to the surface. The determination of LCN2 was performed by using the electroactive property of α-naphthol which is acquired the product from the interaction between alkaline phosphatase and α-naphthyl phosphate. The constructed electrode was characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The aptamer modified GSPE/P(ATT)-GO/AuNPs showed the superior electrocatalytic performance towards the voltammetric determination of LCN2 with a wide linear range (1.0-1000.0 ng/mL) and a low limit of detection (LOD) (0.3 ng/mL). The proposed aptasensor revealed the excellent sensitivity, anti-interference ability and reproducibility which approved that the GSPE/P (ATT)-GO/AuNPs is a promising composite for the sensitive detection of LCN2. The fabricated aptasensor was applied for the determination of LCN2 in fetal bovine serum samples using the standard addition method and the recovery values were in the range of 99.2% and 103.22%.

Facile Synthesis, Characterization of Poly-2-mercapto-1,3,4-thiadiazole Nanoparticles for Rapid Removal of Mercury and Silver Ions from Aqueous Solutions

Industrial pollution by heavy metal ions such as Hg2+ and Ag⁺ is a universal problem owing to the toxicity of heavy metals. In this study, a novel nano-adsorbent, i.e., poly-2-mercapto-1,3,4-thiadiazole (PTT), was synthesized and used to selectively adsorb mercury and silver ions from aqueous solutions. PTT nanoparticles were synthesized via chemical oxidative dehydrogenation polymerization under mild conditions. Oxidant species, medium, monomer concentration, oxidant/monomer molar ratio, and polymerization temperature were optimized to obtain optimum yields. The molecular structure and morphology of the nanoparticles were analyzed by ultraviolet-visible (UV-Vis), Fourier transform infrared (FT-IR), matrix-assisted laser desorption/ionization/time-of-flight (MALDI/TOF) mass and X-ray photoelectron (XPS) spectroscopies, wide-angle X-ray diffraction (WAXD), theoretical calculations and transmission electron microscopy (TEM), respectively. It was found that the polymerization of 2-mercapto-1,3,4-thiodiazole occurs through head-to-tail coupling between the S(2) and C(5) positions. The PTT nanoparticles having a peculiar synergic combination of four kinds of active groups, S⁻, ⁻SH, N⁻N, and =N⁻ with a small particle size of 30⁻200 nm exhibit ultrarapid initial adsorption rates of 1500 mg(Hg)·g-1·h-1 and 5364 mg(Ag)·g-1·h-1 and high adsorption capacities of up to 186.9 mg(Hg)·g-1 and 193.1 mg(Ag)·g-1, becoming ultrafast chelate nanosorbents with high adsorption capacities. Kinetic study indicates that the adsorption of Hg2+ and Ag⁺ follows the pseudo-second-order model, suggesting a chemical adsorption as the rate-limiting step during the adsorption process. The Hg2+ and Ag⁺-loaded PTT nanoparticles could be effectively regenerated with 0.1 mol·L-1 EDTA or 1 mol·L-1 HNO₃ without significantly losing their adsorption capacities even after five adsorption⁻desorption cycles. With these impressive properties, PTT nanoparticles are very promising materials in the fields of water-treatment and precious metals recovery.

Highly Productive Synthesis, Characterization, and Fluorescence and Heavy Metal Ion Adsorption Properties of Poly(2,5-dimercapto-1,3,4-thiadiazole) Nanosheets

Poly(2,5-dimercapto-1,3,4-thiadiazole) (PBT) nanosheets were synthesized by chemical oxidative synthesis under mild conditions. The media, oxidant species, monomer concentrations, oxidant/monomer molar ratio, and temperature were optimized to achieve higher yields and better performance. The molecular structure, morphology, and properties of the nanosheets were analyzed by Fourier transform infrared (FT-IR), ultraviolet-visible (UV-Vis), and fluorescence spectroscopies, wide-angle X-ray diffraction (WAXD), matrix-assisted laser desorption/ionization/time-of-flight (MALDI-TOF) mass spectrometry, X-ray photoelectron spectroscopy (XPS), scanning electronic microscopy (SEM), transmission electron microscopy (TEM), and simultaneous thermogravimetry and differential scanning calorimetry (TG-DSC). It was found that the polymerization of 2,5-dimercapto-1,3,4-thiadiazole occurs via dehydrogenation coupling between two mercapto groups to form the ⁻S⁻S⁻ bond. PBTs show the highest polymerization yield of up to 98.47% and form uniform nanosheets with a thickness of 89~367 nm. poly(2,5-dimercapto-1,3,4-thiadiazole) polymers (PBTs) exhibit good chemical resistance, high thermostability, interesting blue-light emitting fluorescence, and wonderful heavy metal ion adsorption properties. Particularly, the PBT nanosheets having a unique synergic combination of three kinds of active ⁻S⁻, ⁻SH, and =N⁻ groups with a moderate specific area of 15.85 m² g^-1 exhibit an ultra-rapid initial adsorption rate of 10,653 mg g^-1 h^-1 and an ultrahigh adsorption capacity of up to 680.01 mg g^-1 for mercury ion, becoming ultrafast chelate nanosorbents with a high adsorption capacity. With these impressive properties, PBT nanosheets are very promising materials in the fields of water treatment, sensors, and electrodes.

A new class of electropolymerized conducting film from the pyrimidine family for the simultaneous determination of ascorbic acid and dopamine

We report the electropolymerization of 4-amino-6-hydroxy-2-mercaptopyrimidine on a glassy carbon electrode and its application for simultaneous as well as the selective determination of ascorbic acid and dopamine at pH 4.

Electrocatalytic oxidation of ascorbic acid using a poly(aniline-co-m-ferrocenylaniline) modified glassy carbon electrode

A poly(aniline-co-m-ferrocenylaniline) was successfully synthesized on a glassy carbon electrode (GCE) by electrochemical copolymerization using a scan potential range from −0.3 to +0.9 V (vs. Ag/AgCl) in 0.5 M H₂SO₄ containing 30% acetonitrile (ACN), 0.1 M aniline (Ani) and 0.005 M m-ferrocenyaniline (m-FcAni). The field emission scanning electron microscope (FESEM) and electrochemical methods were used to characterize the poly(Ani-co-m-FcAni) modified electrode. The poly(Ani-co-m-FcAni)/GCE exhibited excellent electrocatalytic oxidation of ascorbic acid (AA) in citrate buffer solution (CBS, pH 5.0). The anodic peak potential of AA was shifted from +0.55 V at the bare GCE to +0.25 V at the poly(Ani-co-m-FcAni)/GCE with higher current responses than those seen on the bare GCE. The scan number at the 10th cycle was selected as the maximum scan cycle in electrochemical polymerization. The limit of detection (LOD) was estimated to be 2.0 μM based on the signal-to-noise ratio (S/N = 3). The amperometric responses demonstrated an excellent selectivity for AA determination over glucose (Glu) and dopamine (DA).