Simultaneous determination of Cu2+, Zn2+, Cd2+, Hg2+ and Pb2+ by using second-derivative spectrophotometry method

Anchoring zinc-doped carbon dots on a paper-based chip for highly sensitive fluorescence detection of copper ions

In this work, zinc-doped carbon dots (Zn-CDs) were anchored on a three-dimensional wheel type paper-based microfluidic chip, and were decorated with 6-mercaptonicotinic acid (MNA) and L-cysteine (L-Cys) for highly sensitive and rapid fluorescence detection of Cu²⁺. Zn-CDs were first anchored on paper through the amide bonds between the carboxyl groups of the Zn-CDs and the amino groups of the paper. Afterwards, Zn-CDs were decorated with MNA and L-Cys, effectively preventing the Zn-CDs from aggregation. The nitrogen atom on the pyridine ring and the carboxylic acid groups in MNA and L-Cys coordinated with Cu²⁺ to form a nonfluorescent ground-state complex, causing the fluorescence quenching of the Zn-CDs. The three-dimensional rotary design could simplify the operation process and achieve simultaneous analysis of multiple samples with different concentrations. Under optimal conditions, the fluorescent sensor exhibits linear response for the determination of Cu²⁺ in the range from 0.1 to 60 μg L^-1 with the detection limit (LOD) of 0.018 μg L^-1. The proposed strategy provides a novel way for the highly sensitive detection of Cu²⁺ in a complex water environment.

Laser-Induced Carbon Electrodes in a Three-Dimensionally Printed Flow Reactor for Detecting Lead Ions

Nowadays, heavy metal pollution has attracted wide attention. Many electrochemical methods have been developed to detect heavy metal ions. The electrode surface usually needs to be modified, and the process is complicated. Herein, we demonstrate the fabrication of electrodes by direct laser sintering on commercial polymer films. The prepared porous carbon electrodes can be used directly without any modification. The electrodes were fixed in a 3D-printed flow reactor, which led to very little analyte required during the detection process. The velocities of the analyte under stirring and flowing conditions were simulated numerically. The results prove that flow detection is more conducive to improving detection sensitivity. The limit of detection is about 0.0330 mg/L for Pb²⁺. Moreover, the electrode has been proved to have good repeatability and stability.

Synthesis of N-acetyl-l-cysteine capped Mn:doped CdS quantum dots for quantitative detection of copper ions

In this work, a new assembled copper ions sensor based on the Mn metal-enhanced fluorescence of N-acetyl-l-cysteine protected CdS quantum dots (NAC-Mn:CdS QDs) was developed. The NAC and Mn:CdS QDs nanoparticles were assembled into NAC-Mn:CdS QDs complexes through the formation of CdS and MnS bonds. As compared to NAC capped CdS QDs, higher fluorescence quantum yields of NAC-Mn:CdS QDs was observed, which is attributed to the surface plasmon resonance of Mn metal. In addition, the fluorescence intensity of as-formed complexes weakened in the presence of copper ions. The decrease in fluorescence intensity presented a linear relationship with copper ions concentration in the range from 0.16-3.36μM with a detection limit of 0.041μM . The characterization of as-formed QDs was analyzed by photoluminescence (PL), ultra violet-visible (UV-vis), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and energy dispersive spectroscopy (EDS) respectively. Furthermore, the recoveries and relative standard deviations of Cu²⁺ spiked in real water samples for the intra-day and inter-day analyses were 88.20-117.90, 95.20-109.90, 0.80-5.80 and 1.20-3.20%, respectively. Such a metal-enhanced QDs fluorescence system may have promising application in chemical and biological sensors.

Large-Area Graphene Nanodot Array for Plasmon-Enhanced Infrared Spectroscopy

Graphene nanodot arrays (GNDAs) are fabricated by block copolymer lithography in a high-throughput manner. The GNDA shows strong broadband plasmonic resonances in the mid-IR region with high localized field enhancement, thus allowing plasmon-enhanced infrared spectroscopy with reliable sensitivity and selectivity to be performed.

Electrochemiluminescence-based detection method of lead(II) ion via dual enhancement of intermolecular and intramolecular co-reaction

A novel analytical method to design a highly selective and sensitive detection technique for lead(II) ions (Pb(2+)) detection was developed based on an electrochemiluminescence (ECL) sensor, taking advantage of the high specificity of the aptamer for Pb(2+) and the use of both intermolecular and intramolecular co-reaction to achieve signal enhancement. For sensing interface construction, L-cysteine (Cys) and gold nanostructured layers were electrodeposited on the electrode surface successively, which afforded a large surface area to anchor massive thiol-terminated auxiliary probes (APs) via a thiol-Au interaction. Then, a DNA duplex was generated based on the hybridization of the APs with capture probes (CPs, Pb(2+) specific aptamers). In the presence of Pb(2+), Pb(2+)-induced aptamers were released from the DNA duplex via the formation of a Pb(2+)-stabilized G-quadruplex, accompanied by leaving the single CPs on the sensing interface. Herein, the ruthenium(ii) complexes with functional groups of -COOH (Ru-COOH) were covalently bonded on the polyamidoamine dendrimers with amine end groups (PAMAM), which were capped by the high-index-faceted Au nanoparticles (HIFAuNPs) to obtain the ECL signal labels of Ru-PAMAM-HIFAuNPs. Then, the detection probes (DPs) of amino-terminated Pb(2+) specific aptamers were tagged with the Ru-PAMAM-HIFAuNPs. It was demonstrated that the covalent bonding of PAMAM and Ru-COOH could generate a self-enhanced ECL luminophore by an intramolecular co-reaction and the use of a Cys layer modified electrode could enhance the ECL by the intermolecular co-reaction of Cys and Ru-COOH, which lead to a significant enhancement of the ECL response. Based on this analytical method, the ECL signal increased with Pb(2+) concentration which presented a linear relationship in the range 1.0 × 10(-13)-1.0 × 10(-7) M with the detection limit of 4.0 × 10(-14) M. The proposed approach was also successfully utilized for the determination of Pb(2+) in soil samples.

A novel polyvinyl chloride-membrane optical sensor for the determination of Cu(2+) ion based on synthesized (N'(1)E,N'(2)E)-N'(1),N'(2)-bis(pyridine-2-ylmethylene)oxalohydrazide: experimental design and optimization

A copper (Cu(2+)) ion-selective bulk optode was constructed by using (N'(1)E,N'(2)E)-N'(1),N'(2)-bis(pyridine-2-ylmethylene)oxalohydrazide as ionophore and NaTPB in DBP matrices. Central composite design under response surface methodology was applied for the optimization of variables including pH, amount of ligand, amount of additive and response time which significantly affect the response of proposed sensor. At optimum specified conditions, the high stability, reproducibility and relatively long lifetime of the optical sensor suggest its ability for accurate and precise monitoring of Cu(2+) ion content in various real samples over a concentration range of 1.6×10(-6) to 3.17×10(-5)molL(-1) with a limit of detection of 8.1×10(-7)molL(-1) during response time 6.9min. The proposed optical sensor was successfully applied for the determination of Cu(2+) ion in tap water and different samples.