A Turn-ON fluorometric biosensor based on ssDNA immobilized with a metal phenolic nanomaterial for the sequential detection of Pb(ii) and epirubicin cancer drug

Photoelectrochemical analysis of Pb2+ based on Au@PTCA Schottky junction with Pb2+-G quadruplex structure

Herein, a novel photoelectrochemical (PEC) aptasensor using gold nanoparticles@3,4,9,10-perylene tetracarboxylic (Au@PTCA) Schottky junction as the effective optoelectronic material and lead ion (Pb2+)-G quadruplex structure as the efficient quencher was constructed for the detection of Pb2+ with high sensitivity and excellent selectivity. Au@PTCA Schottky junction, which was proposed by the in situ reduction of Au NPs on the PTCA surface, exhibited a strong unidirectional conductivity, which could generate a significantly enhanced PEC signal compared with the pure PTCA. The Pb2+-G quadruplex structure with a large spatial hindrance effect was formed when the target Pb2+ was present owing to the occurrence of the specific recognition between Pb2+ and its aptamer S1. The formation of a Pb2+-G quadruplex structure effectively quenched the initial signal generated by the Au@PTCA Schottky junction, which was derived from restricted electron transport and light transmission. The obtained prominently decreased PEC signal could achieve the quantitative detection of Pb2+ from 0.5 pM to 500 nM, with a low detection limit of 0.17 pM. The preparation time of this PEC aptasensor was 13 h, and the time for PEC measurement depended on the illumination time, which switched off-on-off for 10 s-20 s-10 s. The study proposed here with high sensitivity and excellent selectivity for Pb2+ analysis offered a novel and reliable tool for environmental monitoring related to heavy metal ions.

"Turn-on" fluorescence sensing for sensitively detecting Cr(VI) via a guest exchange process in Cu NCs@MIL-101 composites

Copper nanoclusters (Cu NCs) are a new fluorescent material that is often used for determining metal ions, but most sensing systems are based on the "turn-off" model. Here, a "turn-on" model of fluorescence sensing for the detection of Cr(VI) was developed based on Cu NCs@MIL-101 composites. The Cu NCs@MIL-101 composites were synthesized from a simple mixture of Cu NCs and MIL-101(Cr), in which the Cu NCs were uniformly distributed in MIL-101(Cr). Notably, the fluorescence intensity of Cu NCs@MIL-101 was significantly weakened due to the internal filtration effect (IFE) of MIL-101. When Cr(VI) was introduced, the fluorescence of Cu NCs@MIL-101 was recovered by the guest exchange process between Cr(VI) and the Cu NCs, which overcame the IFE of Cu NCs@MIL-101. Based on this, a "turn-on" fluorescence probe was successfully constructed for the quantitative detection of Cr(VI) with two linear ranges of 0.05-1 μM and 1-20 μM, and a low detection limit of 0.05 μM. The proposed fluorescence probe possessed excellent selectivity and anti-interference ability, and was successfully applied for the detection of Cr(VI) in real water samples with satisfactory results. This study provides a new approach for the analytical application of Cu NCs.

"Off/On" Fluorescent Probe based on Aggregation-Induced Quenching of ZnO-Quantum dots for Determination of Ara-C: Pharmacokinetic Applications, Adsorption Kinetics & Green Profile Assessment

Herein, a turn "Off/On" fluorescence probe based on ZnO quantum dots (ZnO-QDs) has been proposed and successfully utilized for the determination of Ara-C (cytarabine) using ceric ions (Ce4+) as quencher and ethylenediamine (ED) as a linker. The probe is based initially on the quenching effect of Ce4+ ions on the strong native fluorescence of ZnO-QDs forming the Turn Off system (Ce@ZnO-QDs) that believed to occur due to the aggregation-induced quenching (AIQ) mechanism. The second step is the addition of Ara-C in the presence of ethylenediamine (ED) that encourages the formation of Ara-C/ED/Ce4+ as well as the release of the free ZnO-QDs, leading to the recovery of the fluorescence intensity. The developed sensing platform shows a linear response towards Ara-C over the range of 10 to 1000 ng mL-1 giving a limit of detection (LOD) and limit of quantitation (LOQ) of 1.22 ng mL-1 and 3.70 ng mL-1, respectively. A dispersive magnetic solid phase micro-extraction (dMSPE) method was developed and optimized for the extraction of Ara-C in spiked human plasma using thiol-modified magnetite nanoparticles (S-MNPs). The proposed platform exhibits good sensitivity toward Ara-C in the presence of different interfering substances. Excellent recoveries are obtained after spiking different concentrations of Ara-C into rabbit plasma samples. The validated experimental parameters have been successfully applied to monitor the pharmacokinetic profile of Ara-C in rabbit plasma. A detailed adsorption kinetics study has been carried out to provide a deep insight into the adsorption behavior of Ara-C on the thiol-doped-magnetite nanoparticles. The greenness assessment of the proposed method was achieved and compared with other reported methods using two tools of greenness; the green analytical procedure index (GAPI) and the analytical greenness calculator AGREE.

Mo5N6 nanosheets for fluorescent quenching and target recognition: Highly selectively sensing of sodium hexametaphosphate

Typical fluorescent biosensors use fluorescently labeled ssDNA for target recognition and nanomaterials for signal transduction. Herein, we propose a reverse sensing strategy that Mo5N6 nanosheets are used for target recognition while fluorescein (FAM)-labeled ssDNA only serves for signal generation. We discover that Mo5N6 nanosheets show high fluorescence quenching ability (>95%) and selective recognition for sodium hexametaphosphate (SHMP). After FAM-labeled ssDNA is adsorbed on Mo5N6 nanosheets, the fluorescence is quenched due to the photoinduced electron transfer (PET) effect between FAM and Mo5N6 nanosheets. SHMP can specifically displace the adsorbed FAM-labeled ssDNA from Mo5N6 nanosheets, resulting in more than 80% fluorescence recovery on addition of 5 μmol L-1 SHMP. This biosensor can sensitively detect SHMP down to 150 nmol L-1 and selectively recognize SHMP over glucose, lactose, common amino acids, Zn2+, Mg2+, Ca2+ and other phosphates (such as Na2HPO4, sodium pyrophosphate, sodium tripolyphosphate). This biosensor also shows great potential for the detection of SHMP in bacon sample. This work not only provides a facile sensitive and selective biosensor for SHMP but also exploits the application of transition metal nitrides in the field of sensing and biosensing.

High-sensitivity detection of low-concentration heavy metal ions in solution by multiple reflection enhanced absorption (MREA) spectroscopy

Heavy metal ions (Cr6+, Co2+, Ni2+, and Cu2+) in the electroplating and electrolysis industries are significantly related to process parameters and product quality, even at lower concentrations. Absorption spectroscopy is widely used for substance qualitative and quantitative analysis, which is an analytical method with the potential for real-time monitoring of heavy metal ions concentration in industrial processes. In this paper, a low-concentration heavy metal ion analysis method based on multiple reflection enhanced absorption (MREA) is proposed. Compared with traditional absorption, MREA has the advantages of low concentration detection limit and high-sensitivity. First, a reflective film (Al-SiO2) was prepared and a multiple reflection optical structure was designed to realize multiple parallel reflections of light in the solution medium. Then absorption spectra of low-concentration Cr6+, Co2+, Ni2+ and Cu2+ solutions were measured by MREA and traditional absorption methods. Finally, spectral bandwidth and incident light spots were optimized to obtain a superior absorption enhancement effect. The results showed that MREA could effectively increase the substance absorbance compared with traditional absorption. At the same time, with the optimal spectral bandwidth (0.4 nm) and incident light spot (1 mm), the detection limit of Cr6+, Co2+, Ni2+ and Cu2+ was reduced by 81.48%, 82.52%, 80.92% and 82.93%, respectively. The sensitivity was improved by 5-6 times, which was more obvious for low-concentration detection. In addition, the MREA method can achieve ion concentration analysis when Cr6+, Co2+, Ni2+, and Cu2+ coexist, and the linear correlative coefficients of the C-A curves were all greater than 0.999. Moreover, by adjusting reflectivity of the reflective film and the number of reflections in the optical structure, the results of the MREA method can be further optimized for the low-concentration heavy metal ion analysis. The MREA method has the advantages of simplicity, rapidity and versatility, which can provide the technical foundation for real-time monitoring method development of low-concentration heavy metal ions in industrial processes.

A sensitive sensor based on carbon dots for the determination of Fe3+ and ascorbic acid in foods

To develop a feasible, sensitive, and essential sensor is important for the identification of Fe3+ ions and ascorbic acid (AA). Herein, highly fluorescent heteroatom co-doped carbon dots (N,S-CDs) with a quantum yield (QY) of 24.6% were synthesized, using hydrothermal treatment of L-cysteine (Cys) and 1-amino-2-naphthol-4-sulfonic acid (ANSA). The fluorescence emission of the as-prepared N,S-CDs was quenched strongly by Fe3+ ions, and this was further recovered by the reduction effect of AA on Fe3+. Based on this, continuous fluorescence sensing of Fe3+ and AA with an "on-off-on" style was developed. The detection of Fe3+ and AA were in relatively wider linear ranges of 5.00-105 μmol L-1 and 4.97-54.8 μmol L-1, with a detection limit of 0.10 μmol L-1 and 2.4 nmol L-1 (S/N = 3), respectively. Then, the N,S-CDs were successfully used to measure Fe3+ ions and AA in some daily food samples, and this method exhibited some advantages over most other reported techniques in the term of response speed, quantum yield, and detection limit.

Toward a Selective Analysis of Heavy Metal Salts in Aqueous Media with a Fluorescent Probe Array

Detection of heavy meals in aqueous media challenges worldwide research in developing particularly fast and affordable methods. Fluorescent sensors look to be an appropriate instrument for such a task, as recently they have been found to have made large progress in the detection of chemical analytes, primarily in the environment, along with biological fluids, which still suffer from not enough selectivity. In this work, we propose a new fluorescent method to selectively recognize heavy metals in an aqueous solution via employing an array of several fluorescent probes: acridine yellow, eosin, and methylene blue, which were taken as examples, being sensitive to a microsurrounding of the probe molecules. The exemplary sensor array generated six channels of spectral information through the use of various combinations of excitation and detection wavelengths. Following the known multisensor approach, we applied a linear discriminant analysis to selectively distinguish the vector signals from the sensor array from salts of heavy metals-Cu, Pb, Zn, Cd, and Cz-at the concentration ranges of 2.41 × 10^-6-1.07 × 10^-5 M, 2.8 × 10^-5-5.87 × 10^-4 M, 1.46 × 10^-6-6.46 × 10^-6 M, 1.17 × 10^-8-5.2 × 10^-8 M, and 2.11 × 10^-6-9.33 × 10^-6 M, respectively. The suggested approach was found to be promising due to it employing only one cuvette containing the test solution, simplifying a sample preparation when compared to preparing a variety of solutions in tests with single fluorescence probes.

Dual fluorometric biosensor based on a nanoceria encapsulated metal organic framework and a signal amplification strategy of a hybridization chain reaction for the detection of melamine and Pb2+ ions in food samples

The increased need for melamine and Pb2+ ion detection systems that are versatile, ultra-sensitive, and easy to use is highly significant.

Recyclable Target Metal-Enhanced Fluorometric Naked Eye Aptasensor for the Detection of Pb2+ and Ag+ Ions Based on the Structural Change of CaSnO3@PDANS-Constrained GC-Rich ssDNA

Reliable, label-free, and ultraselective detection of Pb2+ and Ag+ ions is of paramount importance for toxicology assessment, human health, and environmental protection. Herein, we present a novel recyclable fluorometric aptasensor based on the Pb2+ and Ag+-induced structural change of the GC-rich ssDNA (guanine cytosine-rich single-strand DNA) and the differences in the fluorescence emission of acridine orange (AO) from random coil to highly stable G-quadruplex for the detection of Pb2+ and Ag+ ions. More interestingly, the construction and principle of the aptasensor explore that the GC-rich ssDNA and AO can be strongly adsorbed on the CaSnO3@PDANS surface through the π-π stacking, hydrogen-bonding, and metal coordination interactions, which exhibit high fluorescence quenching and robust holding of the GC-rich ssDNA. However, in the presence of Pb2+, the specific G-rich ssDNA segment could form a stable G-quadruplex via G4-Pb2+ coordination and capture of AO from the CaSnO3@PDANS surface resulting in fluorescence recovery (70% enhancement). The subsequent addition of Ag+ ion induces coupled cytosine base pairs in another segment of ssDNA to get folded into a duplex structure together with the G-quadruplex, which highly stabilizes the G-quadruplex resulting in the maximum recovery of AO emission (99% enhancement). When the Cys@Fe3O4Nps are added to the above solution, the sensing probe was restored by complexation between the Cys in the Cys@Fe3O4Nps and target metal ions, resulting in the fabrication of a highly sensitive recyclable Pb2+ and Ag+ assay with detection limits of 0.4 and 0.1 nM, respectively. Remarkably, the Cys@Fe3O4Nps can also be reused after washing with EDTA. The utility of the proposed approach has great potential for detecting the Pb2+ and Ag+ ions in environmental samples with interfering contaminants.

High Catalytic Activity of Fluorophore-Labeled Y-Shaped DNAzyme/3D MOF-MoS2NBs as a Versatile Biosensing Platform for the Simultaneous Detection of Hg2+, Ni2+, and Ag+ Ions

In this study, we have designed a three-fluorophore-labeled Y-shaped DNAzyme with a high catalytic cleavage activity and a three-dimensional (3D) MOF-MoS₂NB (metal-organic framework fused with molybdenum disulfide nanobox), which was synthesized as an efficient quencher of the fluorescent biosensor. The synthesized porous 3D MOF-MoS₂NBs and Y-shaped DNAzyme exhibited a good analytical response toward the simultaneous multiple detections of Hg²⁺, Ni²⁺, and Ag⁺ ions over the other coexisting metal ions. More specifically, the three kinds of enzyme aptamer and substrate aptamer (SA) were hybridized and annealed to form the Y-shaped DNAzyme structure and labeled with three different fluorophores such as FAM, TAMRA, and ROX over the 3'-end of SA. When the targets were induced, the DNAzyme was triggered to cleave the fluorophore-labeled SAs. Then, the cleaved SAs (FAM-SA, TAMRA-SA, and ROX-SA) were adsorbed on the 3D MOF-MoS₂NB surface to quench the fluorescence signal due to a noncovalent interaction (van der Waals and π-π stacking interaction), which transmuted the fluorescence on-state to off-state. As a result, the fluorescence assay confiscated the high selectivity and sensitivity for the target analytes of Hg²⁺, Ni²⁺, and Ag⁺ ions achieved for the detection limits of 0.11 nM, 7.8 μM, and 0.25 nM, respectively. Accordingly, the sensitivity of the developed sensor was explored with a better lower detection limit than the previously reported biosensors. The utility of the designed Y-shaped DNAzyme may find a broad field of application in real water sample analysis with interfering contaminants.

Optical biosensors - Illuminating the path to personalized drug dosing

Optical biosensors are low-cost, sensitive and portable devices that are poised to revolutionize the medical industry. Healthcare monitoring has already been transformed by such devices, with notable recent applications including heart rate monitoring in smartwatches and COVID-19 lateral flow diagnostic test kits. The commercial success and impact of existing optical sensors has galvanized research in expanding its application in numerous disciplines. Drug detection and monitoring seeks to benefit from the fast-approaching wave of optical biosensors, with diverse applications ranging from illicit drug testing, clinical trials, monitoring in advanced drug delivery systems and personalized drug dosing. The latter has the potential to significantly improve patients' lives by minimizing toxicity and maximizing efficacy. To achieve this, the patient's serum drug levels must be frequently measured. Yet, the current method of obtaining such information, namely therapeutic drug monitoring (TDM), is not routinely practiced as it is invasive, expensive, time-consuming and skilled labor-intensive. Certainly, optical sensors possess the capabilities to challenge this convention. This review explores the current state of optical biosensors in personalized dosing with special emphasis on TDM, and provides an appraisal on recent strategies. The strengths and challenges of optical biosensors are critically evaluated, before concluding with perspectives on the future direction of these sensors.