Resonance light scattering sensor of the metal complex nanoparticles using diethyl dithiocarbamate doped graphene quantum dots for highly Pb(II)-sensitive detection in water sample

A dual-mode method for detection of miRNA based on the photoluminescence and resonance light scattering

MicroRNAs (miRNAs) hold potential as useful biomarkers for early diagnosis and evaluation of diverse cancers, but their low abundance and short length make the detection of miRNAs face low sensitivity and accuracy. Herein, a photoluminescence (PL)-resonance light scattering (RLS) dual-mode method was developed for the sensitive and accurate detection of miRNA-141 using CdTe quantum dots (QDs) and Au nanoparticles. The presence of miRNA-141 induced PL quenching and RLS increasing. The limit of detection (LOD) was as low as 3.7 fM, and the miRNA-141 was detected linearly in a range from 10 fM to 10 nM. The dual signals generated no mutual interference and were detected using the same spectrophotometer, allowing for mutual validation to ensure the accuracy and reliability of the detection results. This study proposes valuable references for constructing dual-mode detection methods.

One-Step Hydrothermal Synthesis of Highly Fluorescent MoS2 Quantum Dots for Lead Ion Detection in Aqueous Solutions

Lead ions in water are harmful to human health and ecosystems because of their high toxicity and nondegradability. It is important to explore effective fluorescence probes for Pb²⁺ detection. In this work, surface-functionalized molybdenum disulfide quantum dots (MoS₂ QDs) were prepared using a hydrothermal method, and ammonium tetrathiomolybdate and glutathione were used as precursors. The photoluminescence quantum yield of MoS₂ QDs can be improved to 20.4%, which is higher than that for MoS₂ QDs reported in current research. The as-prepared MoS₂ QDs demonstrate high selectivity and sensitivity for Pb²⁺ ions, and the limit of detection is 0.056 μM. The photoluminescence decay dynamics for MoS₂ QDs in the presence of Pb²⁺ ions in different concentrations indicate that the fluorescence quenching originated from nonradiative electron transfer from excited MoS₂ QDs to the Pb²⁺ ion. The prepared MoS₂ QDs have great prospect and are expected to become a good method for lead ion detection.

Metal ion sensing with graphene quantum dots: detection of harmful contaminants and biorelevant species

Graphene quantum dots (GQDs) are attractive materials for use as highly selective and sensitive chemical sensors, owing to their simple preparation and affordability. GQDs have been successfully deployed as sensors for toxic metal ions, which is a significant issue due to the ever-increasing environmental contamination from agricultural and industrial activities. Despite the success of GQDs in this area, the mechanisms which underpin GQD-metal ion specificity are rarely explored. This lack of information can result in difficulties when attempting to replicate published procedures and can limit the judicious design of new highly selective GQD sensors. Furthermore, there is a dearth of GQD examples which selectively detect biologically relevant alkali and alkaline earth metals. This review will present the current state of GQDs as metal ion sensors for harmful contaminants, highlighting and discussing the discrepancies that exist in the proposed mechanisms regarding metal ion selectivity. The emerging field of GQD sensors for biorelevant metal ion species will also be reviewed, with a perspective to the future of this highly versatile material.

Selective Fe(ii)-fluorescence sensor with validated two-consecutive working range using N,S,I-GQDs associated with garlic extract as an auxiliary green chelating agent

The goal of this work was to use the pyrolysis process to synthesize graphene quantum dots doped with garlic extract (as N,S-GQDs) and simultaneously co-doped with iodine (as I-GQDs). XPS, HR-TEM, FE-SEM/EDX, FT-IR, fluorescence, and UV-visible absorption spectroscopy were used to characterize the N,S,I-GQDs and analyze their morphological images. The quantum yield of N,S,I-GQDs was found to be 45%, greater than that of undoped GQDs (31%). When stimulated at 363 nm, the N,S,I-GQDs display a strong fluorescence intensity at a maximum wavelength of 454 nm. Using N,S,I-GQDs as a fluorescence quenching sensor for screening tests with various metal ions, it was discovered that they are extremely selective towards Fe2+ over Fe3+ and other ions. Thus, solution pH, concentration of N,S,I-GQDs, quantity of garlic extract, EDTA and AgNO3 concentration as masking agents, reaction duration under ultrasonic aid, and tolerable limit of Fe3+ presence in the target analyte were all optimized for Fe2+ detection. A highly sensitive detection of Fe2+ was obtained using a linear curve with y = 141.34x + 5.5855, R 2 = 0.9961, LOD = 0.11 mg L-1, and LOQ = 0.35 mg L-1. The method precision, given as RSDs, was determined to be satisfactory at 1.04% for intra-day analysis and 3.22% for inter-day analysis, respectively. As a result, the selective determination of trace amounts of Fe2+ in real water samples using such labile multi-element doped GQDs in conjunction with garlic extract as a green chelating agent to maintain its enhanced sensitivity was successfully applied with good recoveries ranging from 89.16 to 121.45%.

Hydrophilic graphene quantum dots as turn-off fluorescent nanoprobes for toxic heavy metal ions detection in aqueous media

Efforts are being made to develop fast, cost-effective and sensitive sensor to detect water contamination by toxic heavy metal ions. The oxygenated functional groups decorated graphene quantum dots (GQDs) effectively enhances the aqueous solubility and considered as a more desirable and simple sensing material with high sensitivity. Here, photoluminescence (PL) property of GQDs has been employed to devise an optical nanosensor for the detection of toxic heavy metal ions in aqueous media. Hydrothermal method was employed to synthesize highly fluorescent and water soluble GQDs. The fluorescence intensity reduces with the increase in toxic heavy metal ions concentration. The observed PL was analyzed by the Stern-Volmer equation to study the fluorescent quenching mechanism of the system. Nonlinear behavior of Stern-Volmer plot suggests that the reduction in the fluorescent intensity is due to the combination of dynamic and static processes. The fluorescence quenching results showed that, the as synthesized GQDs are an efficient fluorescent probe for heavy metal ions viz. Hg²⁺, Cd²⁺ and Pb²⁺ with the detection limit of 1.171 μM, 2.455 μM and 2.011 μM respectively. This study shows the viability of GQDs as promising material for sensing the heavy metal ions in aqueous solution.

Quantum Dots Based Fluorescent Probe for the Selective Detection of Heavy Metal Ions

Heavy metal ions are one of the primary causes of environmental pollution. A marshal effect of heavy metal ions is a paramount ultimatum to humans, aquatic animals and other organisms present in nature. Multitude arrays of materials have been proclaimed for sensing of heavy metal ions and also many methodologies are applied for heavy metal ion sensing. Due to their toxicity and non-biodegradability, it is required to be perceived immediately prior to its manifestation of harmful effects. Quantum Dots (QDs) are zero-dimensional nanomaterial particles and owing to their distinctive optical and electronic properties, they are utilized as nanosensors. QDs have enriched fluorescence properties which includes broad excitation spectrum, narrow emission spectrum and photostability. QDs offer eclectic and sensitive detection of heavy metal ions due to presence of discrete capping agents and different functional groups present on the surface of the QDs. These capping layers and functional groups attune the sensing capability of the QDs, which leverages the interactions of QDs with various analytes by different mechanisms. This review, comprising of papers from 2011 to 2020,focuses on heavy metal ions sensing potential of various quantum dots and its applicability as a nanosensor for on field heavy metal ions detection in water. Quantum Dots (QDs) based Heavy Metal Detection.

Surface Plasmon Resonance Sensor for Novel Detection of Histidine Based on the Hg2+ Induced Aggregation of AuNPs Followed by Preconcentration with Chitosan Gel as Solid-phase Biosorbent

This research work aims to propose an extraction method using chitosan as the sorbent and gold nanoparticles (AuNPs) as the colorimetric sensor for the development of a simple, cost-effective, rapid, sensitive, and selective detection method for histidine. The colorimetric assay is based on the aggregation of AuNPs in the presence of Hg2+ ions and histidine. The state of AuNPs generally changes from dispersion to aggregation. The change in state is accompanied by a corresponding change in color (from red wine to blue). Therefore, the solid phase extraction (SPE) method using chitosan as the sorbent was used to extract the AuNPs to improve the sensitivity of detection. It was found that the extraction by means of a sensor system using chitosan could increase the detection signal for histidine by 10 times. The calibration curve, which is the plot of absorbance ratio (A650/A528) against the concentration of histidine, shows a linear relation in the concentration range of 100 - 800 nM. The limit of detection (LOD) and limit of quantitation (LOQ) of the method were found to be 99.88 and 107.45 nM, respectively. Good recoveries were also obtained (range: 99.75 - 104.43%) with relative standard deviations (RSDs) below 5.89% in real water samples. Moreover, this method can be used for the selective detection of histidine even in the presence of other amino acids. The proposed method has been successfully used in the determination of histidine in mineral water samples.

Ultratrace Detection of Nickel(II) Ions in Water Samples Using Dimethylglyoxime-Doped GQDs as the Induced Metal Complex Nanoparticles by a Resonance Light Scattering Sensor

This study aimed to synthesize dimethylglyoxime (DMG) (N-source)-doped graphene quantum dots (N-GQDs) via simultaneous pyrolysis of citric acid and 1.0% (w/v) DMG. The maximum excitation wavelength (λmax, ex = 380 nm) of the N-GQD solution (49% quantum yield (QY)) was a red shift with respect to that of bare GQDs (λmax, ex = 365 nm) (46% QY); at the same maximum emission wavelength (λmax, em = 460 nm), their resonance light scattering (RLS) intensity peak was observed at λmax, ex/em = 530/533 nm. FTIR, X-ray photoelectron spectroscopy, XRD, energy-dispersive X-ray spectroscopy, and transmission electron microscopy analyses were performed to examine the synthesized materials. The selective and sensitive detection of Ni2+ using the RLS intensity was performed at 533 nm under the optimum conditions consisting of both 25 mg L-1 N-GQDs and 2.5 mg L-1 DMG in the ammonium buffer solution of pH 9.0. The linearity of Ni2+ was 50.0-200.0 μg L-1 with a regression line, y = 5.031x - 190.4 (r 2 = 0.9948). The limit of detection (LOD) and the limit of quantitation (LOQ) were determined to be 20.0 and 60.0 μg L-1, respectively. The method precision expressed as % RSDs was 4.90 for intraday (n = 3 × 3) and 7.65 for interday (n = 5 × 3). This developed method afforded good recoveries of Ni2+ in a range of 85-108% when spiked with real water samples. Overall, this innovative method illustrated the identification and detection of Ni2+ as a DMG complex with N-GQDs, and the detection was highly sensitive and selective.

A Fluorescence Switching Sensor for Sensitive and Selective Detections of Cyanide and Ferricyanide Using Mercuric Cation-Graphene Quantum Dots

This study aims to use graphene quantum dots (GQDs) as a fluorescence switching sensor (turn on-off) for the simultaneous detection of cyanide (CN-) and ferricyanide [Fe(CN)6]3- in wastewater samples. The GQDs were synthesized by pyrolyzing solid citric acid. The intrinsic blue color of the solution was observed under ultraviolet irradiation. The fluorescence spectrum was maximized at both excitation and emission wavelengths of 370 and 460 nm, respectively. The fluorescence intensity of GQDs decorated with Hg2+ (turn-off mode as the starting baseline) could be selectively turned on in the presence of CN- and once back to turn-off mode by [Fe(CN)6]3-. The fluorescence switching properties were used to develop a fluorescence turn-on-off sensor that could be used to detect trace amounts of CN- and [Fe(CN)6]3- in water samples. For highly sensitive detection under optimum conditions (Britton-Robinson buffer solution in the pH range of 8.0-9.0, linearity ranges of 5.0-15.0 μM (R 2 = 0.9976) and 10.0-50.0 μM (R 2 = 0.9994), respectively, and detection limits of 3.10 and 9.48 μM, respectively), good recoveries in the ranges of 85.89-112.66% and 84.88-113.92% for CN- and [Fe(CN)6]3-, respectively, were recorded. The developed methods were successfully used for the simultaneous and selective detection of CN- and [Fe(CN)6]3- in wastewater samples obtained from local municipal water reservoirs.

Fast and efficient removal of Cr(VI) to ppb level together with Cr(III) sequestration in water using layered double hydroxide interclated with diethyldithiocarbamate

It is still a great challenge to find an eco-friendly, easy-to-synthesize, and cheap adsorbent to rapidly remove Cr(VI) to ppb level in the Cr(VI)-polluted water. Herein, a new layered double hydroxide nanocage intercalated with diethyldithiocarbamate (DDTC-LDH) was fabricated via a facile calcination-rehydration method. The DDTC-LDH rapidly decreased Cr(VI) concentration from 5 to <0.05 mg/L within 35 min, and only a few seconds were required to completely remove it at an initial concentration of 0.5-1 mg/L, primarily attributed to the effective adsorption-reduction of Cr(VI) to Cr(III) by sulfur atoms in CS and CS groups. Attractively, the generated Cr(III) was also quickly removed to below 0.1 mg/L via an opportune Lewis hard-hard interaction with C-SO_x groups produced through CS oxidation. Additionally, Cr(VI) could be removed by DDTC-LDH at a wide pH application range (3.17-10.78) and with weak effects by coexisting anions (Cl^-, NO₃^-, CO₃^2-, SO₄^2-, and PO₄^3-). We systematically analyzed and proposed the mechanisms for Cr(VI) removal by the DDTC-LDH, orderly containing electrostatic attraction, Cr(VI) complexation by sulfur atoms in CS and CS groups, reduction of the Cr(VI) to Cr(III) by the CS and CS groups, and Cr(III) complexation by sulfur atoms in C-SOx groups. Our results provide new insights into the Cr(VI) removal using organosulfur compounds, that is to say, the organosulfur group Lewis hardness increased (from C-S to C-SOx) as the Cr species Lewis hardness increased (from Cr(VI) to Cr(III)), so as to opportunely ensure fast and efficient capture of both Cr(VI) and Cr(III) via Lewis acid-base interactions.

Ultrasonic-assisted recycling of Nile tilapia fish scale biowaste into low-cost nano-hydroxyapatite: Ultrasonic-assisted adsorption for Hg2+ removal from aqueous solution followed by "turn-off" fluorescent sensor based on Hg2+-graphene quantum dots

This study was planned to recycle calcium and the phosphorus-rich Nile tilapia fish scale biowaste into nano-hydroxyapatite (FHAP), using ultrasonic-assisted extraction of calcium and phosphorus from fish scales, which was optimized in term of extraction time, acid concentration, extraction temperature, and ultrasonic power. These two elements were determined simultaneously by inductively coupled plasma atomic emission spectrometry and the FHAP phase was formed upon addition of the extracted element solution in alkaline medium using homogenous precipitation assisted with ultrasound energy. The FHAP adsorbent was characterized by x-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and Brunauer-Emmett-Teller. A combination of FHAP and the ultrasonic method was then used to remove Hg²⁺ from aqueous solution. Four significant variables affecting Hg²⁺ removal, namely, adsorbent dosage, pH, ultrasonic power, and adsorption time, were studied. The results exhibited that the optimal conditions for maximizing the removal of Hg²⁺ were 0.02 g adsorbent dosage, pH 8, 0.4 kW ultrasonic power, 20 min adsorption time, and 30 °C adsorption temperature. The sorption mechanism of Hg²⁺ was revealed by isotherm modeling, indicating that FHAP adsorbent has a potential for Hg²⁺ removal in aqueous media with the maximum adsorption capacity being 227.27 mg g^-1. This adsorption behavior is in agreement with the Langmuir model as reflected by a satisfactory R² value of 0.9967, when the kinetics data were fitted with pseudo-second-order. Therefore, the FHAP could be an alternative adsorbent for the ultrasonic-assisted removal of Hg²⁺ at very high efficiency and within a very short period of time.

Development of Graphene Quantum Dots-Based Optical Sensor for Toxic Metal Ion Detection

About 71% of the Earth's surface is covered with water. Human beings, animals, and plants need water in order to survive. Therefore, it is one of the most important substances that exist on Earth. However, most of the water resources nowadays are insufficiently clean, since they are contaminated with toxic metal ions due to the improper disposal of pollutants into water through industrial and agricultural activities. These toxic metal ions need to be detected as fast as possible so that the situation will not become more critical and cause more harm in the future. Since then, numerous sensing methods have been proposed, including chemical and optical sensors that aim to detect these toxic metal ions. All of the researchers compete with each other to build sensors with the lowest limit of detection and high sensitivity and selectivity. Graphene quantum dots (GQDs) have emerged as a highly potential sensing material to incorporate with the developed sensors due to the advantages of GQDs. Several recent studies showed that GQDs, functionalized GQDs, and their composites were able to enhance the optical detection of metal ions. The aim of this paper is to review the existing, latest, and updated studies on optical sensing applications of GQDs-based materials toward toxic metal ions and future developments of an excellent GQDs-based SPR sensor as an alternative toxic metal ion sensor.