Construction of Effective Nanosensor by Combining Semiconducting Polymer Dots with Diphenylcarbazide for Specific Recognition of Trace Cr (VI) Ion in Water and Vitro

Hexavalent chromium (Cr (VI)) ion, as highly toxic environmental pollution, severely endangers the ecological environment and public health. Herein, a fluorescent nanosensor (PFO-DPC) was constructed by combining semiconducting polymer dots with diphenylcarbazide (DPC) for sensing Cr (VI) ion in aqueous solution and living cells. DPC and poly (styrene-co-maleic anhydride) (PSMA) polymer mixed with polyfluorene (PFO) were utilized for selectively indicating Cr (VI) ion and improving the efficiency of detection, respectively. The presence of Cr (VI) ion effectively turned off the blue and green fluorescence of PFO-DPC in the aqueous environment, and the fluorescence quenching efficiency exhibited a good linear relationship between the range of 0.0 to 2.31 nM (R2 = 0.983) with a limit of detection (LOD) of 0.16 nM. The mechanism of fluorescence quenching could possibly be attributed to the internal filtration effect (IFE). Additionally, PFO-DPC showed a satisfactory performance in monitoring intracellular Cr (VI) ion. Our results indicate that the sensor is promising in various applications.

Biologically inspired catalyst for electrochemical reduction of hazardous hexavalent chromium

An indirect electrochemical detoxification and detection platform has been demonstrated for toxic hexavalent chromium (Cr(vi)) based on the biologically important N-4 macrocycle. The research work describes a simple, green, low-cost and potential way for the synthesis of a new N-4 macrocyclic molecule and the molecule is characterized by various analytical and spectroscopic techniques like elemental analysis, TGA, FT-IR, UV-visible, mass spectrometry and NMR spectroscopies, and cyclic voltammetry. The synthesized molecule was explored for the electrochemical reduction of Cr(vi) using both voltammetric and amperometric methods. Amperometric studies exhibited 50 to 2500 nM linear range and the detection limit and quantification limit are 18 and 50 nM, respectively. The common coexisting metal ions did not interfere with Cr(vi) even in the presence of 40-fold excess interfering ions. The real sample analysis was carried out with the fabricated sensor and successfully quantified a recovery result (98-104%) of Cr(vi) in water. This proposed sensor is helpful in the detection of chromium ions in drinking water and is capable of detecting Cr(vi) in the limits set by the World Health Organization (WHO). In addition, this sensor satisfactorily demonstrated considerable stability and reproducibility.

One-step synthesized fluorescent nitrogen doped carbon dots from thymidine for Cr (VI) detection in water

A novel, simple and low-cost nitrogen doped carbon dots (N-CDs) fluorescent sensor for sensitive detection of Cr (VI) was developed via one-step hydrothermal method using thymidine as carbon source. As-prepared N-CDs exhibited the ability of sensitive and selective detection of Cr (VI) through the inner filter effect (IFE). The performances of N-CDs were investigated with the characterization methods of transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Under the optimized conditions, a good logarithm correlation between the fluorescence intensity of N-CD_S and the concentration of Cr (VI) was obtained ranging from 0.1 μM to 430 μM (R² = 0.992), with a low detection limit (LOD; S/N = 3) of 1.26 nM. The fluorescent sensor showed good repeatability, reproducibility and stability. Furthermore, N-CDs fluorescent sensor had a good applicability for Cr (VI) detection in real water samples with acceptable recoveries, and the detection results were consistent with the inductively coupled plasma mass spectrometry (ICP-MS) results, indicating this fluorescent sensor has a great potential for the environmental monitoring.

Photoelectrochemical Determination of Cu2+ Using a WO3/CdS Heterojunction Photoanode

Copper ions are not only physiologically essential for life but also hazardous materials causing a series of neurodegenerative diseases. Photoelectrochemical (PEC) detection has attracted a large amount of focus as a potential strategy to develop Cu²⁺ ion sensors. However, relatively low photocurrent signals with poor antidisturbance ability and the limited concentration range have prevented its practical applications. Here, we designed a WO₃/CdS heterojunction photoanode for the PEC determination of Cu²⁺ in aqueous solution through a simple two-step chemical bath deposition method. The obtained WO₃/CdS photoanode had a nanoplate morphology and showed an enhanced photoresponsivity with a photocurrent density of 1.5 mA/cm² at 1.23 V versus RHE under illumination. Naturally, it exhibited a low detection limit (0.06 μM) and wider range (0.5 μM to 1 mM) for Cu²⁺ PEC detection first, suggesting that the WO₃/CdS heterojunction photoanode is a promising tool to monitor copper pollution in natural environments.

A sonochemical synthesis of cyclodextrin functionalized Au-FeNPs for colorimetric detection of Cr6+ in different industrial waste water

This paper describes a simple, selective and sensitive colorimetric sensing of Cr⁶⁺ ions using β-Cyclodextrin (β-CD) functionalized gold-iron nanoparticles (β-CD/Au-FeNPs). The sonochemically synthesized nanoparticles are winered in colour due to the SPR band of β-CD functionalized bimetalic nanoparticles Au-FeNPs. The capping and stabilizing of Au-FeNPs by redox β-CD is confirmed by FT-IR. The particles are spherical in shape and it posses the effective diameter of 18-20 nm. Under optimized conditions, in the presence of Cr⁶⁺ the wine red Au-FeNPs solution was turned to colourless, accompanying the broadening and red shifting of SPR band. The ratio between the absorbance wavelength at 573 nm to 535 nm (A₅₇₃/A₅₃₅) is linearly correlated with the Cr⁶⁺ concentrations ranging from 50 nM to 500 nM, with a detection limit of Cr⁶⁺ of 2.5 nM was achieved for the first time using β-CD/Au-FeNPs by spectrophotometry. The selectivity of the β-CD/Au-FeNPs towards other interfering metal ions. Finally the proposed method has been successfully employed for the determination of Cr⁶⁺ ion in various industrial waste water with good recoveries.

Controllable Mn-doped ZnO nanorods for direct assembly of a photoelectrochemical aptasensor

A label-free photoelectrochemical (PEC) aptasensor for K⁺ was first constructed by direct self-assembly of the K⁺ aptamer onto the electrodeposited Mn-doped ZnO nanorods.

Ultrasensitive photoelectrochemical determination of chromium(VI) in water samples by ion-imprinted/formate anion-incorporated graphitic carbon nitride nanostructured hybrid

A rapid and highly sensitive photoelectrochemical (PEC) method has been proposed for the determination of trace amounts of chromium in water samples under visible-light irradiation. Here, a unique nanostructured hybrid of formate anion incorporated graphitic carbon nitride (F-g-C3N4) is smartly integrated with a Cr(VI) ion-imprinted polymer (IIP) as a photoactive electrode (denoted as IIP@F-g-C3N4). The nanohybrid of F-g-C3N4 exhibits an enhanced charge separation with substantially improved PEC responses versus g-C3N4. The newly designed IIP@F-g-C3N4 PEC sensor exhibits high sensitivity and selectivity for the determination of Cr(VI) because it offers efficient photogenerated electron reduction toward Cr(VI). The PEC analysis is highly linear over Cr(VI) concentrations ranging from 0.01 to 100.00ppb with a detection limit of 0.006ppb (S/N=3). Our approach can be used to detect Cr(VI), Cr(III) and the total chromium level in aqueous solution through oxidation of Cr(III) to Cr(VI) and the determination of the total chromium as Cr(VI). In practical applications, this low-cost and sensitive assay has been successfully applied for speciation determination of chromium in environmental water samples.

Photoelectrochemical detection of metal ions

Depending on the situation, metal ions may either play beneficial roles or be harmful to human health and ecosystems. Sensitive and accurate detection of metal ions is thus a critical issue in the field of analytical sciences and great efforts have been devoted to the development of various metal ion sensors. Photoelectrochemical (PEC) detection is an emerging technique for the bio/chemical detection of metal ions, and features a fast response, low cost and high sensitivity. Using representative examples, this review will first introduce the fundamentals and summarize recent progress in the PEC detection of metal ions. In addition, interesting strategies for the design of particular PEC metal ion sensors are discussed. Challenges and opportunities in this field are also presented.

Cadmium Sulphide-Reduced Graphene Oxide-Modified Photoelectrode-Based Photoelectrochemical Sensing Platform for Copper(II) Ions

A photoelectrochemical (PEC) sensor with excellent sensitivity and detection toward copper (II) ions (Cu²⁺) was developed using a cadmium sulphide-reduced graphene oxide (CdS-rGO) nanocomposite on an indium tin oxide (ITO) surface, with triethanolamine (TEA) used as the sacrificial electron donor. The CdS nanoparticles were initially synthesized via the aerosol-assisted chemical vapor deposition (AACVD) method using cadmium acetate and thiourea as the precursors to Cd²⁺ and S^2-, respectively. Graphene oxide (GO) was then dip-coated onto the CdS electrode and sintered under an argon gas flow (50 mL/min) for the reduction process. The nanostructured CdS was adhered securely to the ITO by a continuous network of rGO that also acted as an avenue to intensify the transfer of electrons from the conduction band of CdS. The photoelectrochemical results indicated that the ITO/CdS-rGO photoelectrode could facilitate broad UV-visible light absorption, which would lead to a higher and steady-state photocurrent response in the presence of TEA in 0.1 M KCl. The photocurrent decreased with an increase in the concentration of Cu²⁺ ions. The photoelectrode response for Cu²⁺ ion detection had a linear range of 0.5–120 μM, with a limit of detection (LoD) of 16 nM. The proposed PEC sensor displayed ultra-sensitivity and good selectivity toward Cu²⁺ ion detection.

N-doped TiO2 based visible light activated label-free photoelectrochemical biosensor for detection of Hg(2+) through quenching of photogenerated electrons

A novel photoelectrochemical (PEC) biosensor was fabricated based on N-doped TiO2 for the detection of Hg(2+) through the quenching of photogenerated electrons. The N-doped TiO2 was synthesized by a sol-gel method with urea and tetrabutyl titanate as the N and Ti sources. Compared with the undoped TiO2, the N-doped TiO2 showed an enhanced photocurrent response under visible light (λ > 420 nm). The sensing surface was functionalized with 5'-amino-modified T-rich oligonucleotides. The photoelectrochemical biosensor bound Hg(2+) on the surface by a highly specific T-Hg(2+)-T recognition. Hg(2+) on the surface of the N-doped TiO2 film withdrew the photogenerated electrons and decreased the recorded current signal. The dynamic linear range for Hg(2+) has been determined to be as low as 2-6 μM.

Femtomole level photoelectrochemical aptasensing for mercury ions using quercetin-copper(II) complex as the DNA intercalator

An ultrasensitive and selective photoelectrochemical (PEC) aptasensor for mercury ions was first fabricated based on perylene-3, 4, 9, 10-tetracarboxylic acid/graphene oxide (PTCA/GO) heterojunction using quercetin-copper(II) complex intercalated into the poly(dT)-poly(dA) duplexes. Both the PTCA/GO heterojunction and the quercetin-copper(II) complex are in favor of the sensitivity for the fabricated PEC aptasensor due to band alignment and strong reduction capability, respectively. And they efficiently promote the separation of photoexcited carriers and enhance the photocurrent. The formation of thymine-Hg(2+)-thymine coordination chemistry resulted in the dehybridization of poly(dT)-poly(dA) duplexes and then the intercalator quercetin-copper(II) complex broke away from the surface of the PEC aptasensor. As the concentration of mercury ions increased, the photocurrent gradually decreased. The electrode response for mercury ions detection was in the linear range from 0.01 pmol L(-1) to 1.00 pmol L(-1) with the detection limit of 3.33 fmol L(-1). The label-free PEC aptasensor has excellent performances with ultrasensitivity and good selectivity besides the advantage of economic and facile fabrication. The strategy of quercetin-copper(II) complex as a novel DNA intercalator paves a new way to improve the performances for PEC sensors.