Tuning of gold nanoclusters sensing applications with bovine serum albumin and bromelain for detection of Hg2+ ion and lambda-cyhalothrin via fluorescence turn-off and on mechanisms

Dual-emission copper nanoclusters for hydrogen sulfide detection: a novel approach

Dual-emission copper nanoclusters (CuNCs) were synthesized via a novel, green and one-pot aqueous method, employing bovine serum albumin and glutathione as reducing and stabilizing agents, respectively. The CuNCs exhibited distinct fluorescence emissions at 443 nm and 612 nm under 365 nm excitation. Notably, with the increase in hydrogen sulfide concentration, the dual-emission fluorescence of CuNCs was gradually quenched, and complete quenching occurred at 280 μM. The probe demonstrated a stable response to hydrogen sulfide within the concentration range of 2.5-60.0 μM. The detection limit of hydrogen sulfide was as low as 0.32 μM, which is significantly lower than the limit set by the World Health Organization (1.5 μM). This method was successfully applied for the detection of sulfide in environmental samples, achieving remarkable recovery rates ranging from 98.2-102%. Moreover, the response mechanism and practical application potential of CuNCs as a hydrogen sulfide detection platform were investigated, offering crucial insights for the study of fluorescence properties of metal nanoclusters and the prevention and control of hydrogen sulfide pollution.

Safeguarding food safety: Nanomaterials-based fluorescent sensors for pesticide tracing

Pesticide residue contamination has emerged as a critical concern due to its potential negative effects on both public health and the natural environment. Consequently, the detection of pesticide residue is of utmost importance. Nanomaterial-based fluorescence sensors, including metal nanoparticles (MNPs), metal nanoclusters (MNCs), carbon dots (CDs), and quantum dots (QDs), are particularly effective for detecting pesticide residues. Herein, we provide a comprehensive review of the recent advances (2018-2024) in fluorescence-based sensors utilizing MNPs, MNCs, CDs and QDs and their composites for the purpose of detecting various pesticides including organophosphates, carbamates, organochlorines, and pyrethroids in food. This review delves into the evolution of nanomaterials, their corresponding fluorescence-based sensing mechanisms, including Förster resonance energy transfer (FRET), photoinduced electron transfer (PET), inner filter effect (IFE), aggregation induced emission (AIE), and the detection principle, focusing on aspects of sensitivity and specificity. We also address the challenges and future perspectives of nanomaterials-based fluorescence sensors.

Recent advances in colorimetric and photoluminescent fibrillar devices, photonic crystals and carbon dot-based sensors for mercury (II) ion detection

The escalating environmental contamination with mercury has become a pressing issue, significantly impacting human beings and nature. For instance, small-scale gold mining has led to severe contamination in the Brazilian Yanomami village, highlighting the urgent need for action. The development of fibrillar-based sensors for mercury (II) ions represents an important issue to be considered in the point-of-care and simple detection of contaminants in water. Herein, this review discussed different colorimetric/photoluminescent-based prototypes for Hg2+ ions sensors and corresponding strategies to improve selectivity and sensitivity associated with the regeneration and reuse of the devices. Given these aspects, the electrospinning technique is promising for developing advanced mercury (II) ion sensors.

Development of Copper Nanoclusters-Based Turn-Off Nanosensor for Fluorescence Detection of Two Pyrethroid Pesticides (Cypermethrin and Lambda-Cyhalothrin)

Fluorescent copper nanoclusters (Cu NCs) were synthesized by using Withania somnifera (W. somnifera) plant extract as a biotemplate. Aqueous dispersion of W. somnifera-Cu NCs displays intense emission peak at 458 nm upon excitation at 350 nm. This fluorescence emission was utilized for the detection of two pyrethroid pesticides (cypermethrin and lambda-cyhalothrin) via "turn-off" mechanism. Upon the addition of two pyrethiod pesticides independently, the fluorescence emission of W. somnifera-Cu NCs was gradually decreased with increasing concentrations of both pesticides. It was noticed that the decrease in emission intensity at 458 nm was linearly dependent on the logarithm of both pesticides concentrations in the ranges of 0.01-100 μM and of 0.05-100 μM for cypermethrin and lambda-cyhalothrin, respectively. Consequently, the limits of detection were found to be 27.06 and 23.28 nM for cypermethrin and lambda-cyhalothrin, respectively. The as-fabricated W. somnifera-Cu NCs acted as a facile sensor for the analyses of cypermethrin and lambda-cyhalothrin in vegetables (tomato and bottle gourd), which demonstrates that it could be used as portable sensing platform for assaying of two pyrethroid pesticides in food samples.

An enzymatic activity regulation-based clusterzyme sensor array for high-throughput identification of heavy metal ions

The accurate identification and sensitive quantification of heavy metal ions are of great significance, considering that pose a serious threat to environment and human health. Most array-based sensing platforms, to date, utilize nanozymes as sensing elements, but few studies have explored the application of the peroxidase-like activity of clusterzymes in identification of multiple analytes. Herein, for the first time, we developed a clusterzyme sensor array utilizing gold nanoclusters (AuNCs) as sensing elements for five heavy metal ions identification including Hg²⁺, Pb²⁺, Cu²⁺, Cd²⁺ and Co²⁺. The heavy metal ions can differentially regulate the peroxidase-like activity of AuNCs, and that can be converted into colorimetric signals with 3,3',5,5'-tetramethylbenzidine (TMB) as the chromogenic substrate. Subsequently, the generated composite responses can be interpreted by combining pattern recognition algorithms. The developed clusterzyme sensor array can identify five heavy metal ions at concentrations as low as 0.5 μM and their multi-component mixtures. Especially, we demonstrated the successful identification of multiple heavy metal ions in tap water and traditional Chinese medicine, with an accuracy of 100% in blind test. This study provided a simple and effective method for identification and quantification of heavy metal ions, rendering a promising technique for environmental monitoring and drug safety assurance.

Recent advances in the biomolecules mediated synthesis of nanoclusters for food safety analysis

The development of nanoclusters based on incorporating biomolecules like proteins, lipids, enzymes, DNA, surfactants, and chemical stabilizers creates a stable and high fluorescence bio-sensors promising future due to their high sensitivity, high level of detection and better selectivity. This review addresses a comprehensive and systematic overview of the recent development in synthesizing metal nanocluster by various strategized synthesis techniques. Significantly, the application of nanometal clusters for the detection of various food contaminants such as microorganisms, antibodies, drugs, pesticides, metal contaminants, amino acids, and other food flavors have been discussed briefly concerning the detection techniques, sensitivity, selectivity, and lower limit of detection. The review further gives a brief account on the future prospects in the synthesis of novel metal nanocluster-based biosensors, and their advantages, shortcomings, and potential perspectives toward their application in the field of food safety analysis.

Quantum confined peptide assemblies in a visual photoluminescent hydrogel platform and smartphone-assisted sample-to-answer analyzer for detecting trace pyrethroids

Quantum confinement (QC) effect-related materials have been extensively studied as photoluminescent probes for agricultural, food, and environmental analyses, with the advantage of simple-to-synthesize, reusable, nontoxic, and environmentally friendly. Herein, we propose a strategy to dimerize aromatic cyclo-dipeptides, namely cyclo-ditryptophan (cyclo-WW), cyclo-diphenylalanine (cyclo-FF), and cyclo-dihistidine (cyclo-HH), into quantum dots as basic building blocks for the self-assembly of QC supramolecular structures with excellent photoluminescent properties in aqueous solutions. In particular, through coordination with Zn(II), the bandgap can be tuned to change the photo-absorption and luminescence properties of the cyclo-dipeptide-based QC assemblies. The fluorescence quantum yield of cyclo-WW+Zn(II) was 16.9%. Such a good luminous effect makes it applicable to the detection of LC. A good linear relationship between fluorescence response of cyclo-WW+Zn(II) and LC concentration was observed in the range of 5-350 μg/L, with a low limit of detection of 2.9 μg/L and good spiked recovery of 90.72%-104.3%. A visual platform using the cyclo-WW+Zn(II)-based photoluminescent hydrogel and smartphone-assisted sample-to-answer analyzer were developed, which showed good responsiveness to LC. The developed fluorescence method, validated using traditional HPLC, is a biocompatible alternative for the rapid detection of trace pollutants with the advantages of portability and simple operation.

Synthesis of metal nanoclusters and their application in Hg2+ ions detection: A review

Mercuric (Hg²⁺) ions released from human activities, natural phenomena, and industrial sources are regarded as the global pollutant of world's water. Hg²⁺ ions contaminated water has several adverse effects on human health and the environment even at low concentrations. Therefore, rapid and cost-effective method is urgently required for the detection of Hg²⁺ ions in water. Although, the current analytical methods applied for the detection of Hg²⁺ ions provide low detection limit, they are time consuming, require expensive equipment, and are not suitable for in-situ analysis. Metal nanoclusters (MNCs) consisting of several to ten metal atoms are important transition missing between single atoms and plasmonic metal nanoparticles. In addition, sub-nanometer sized MNCs possess unique electronic structures and the subsequent unusual optical, physical, and chemical properties. Because of these novel properties, MNCs as a promising material have attracted considerable attention for the construction of selective and sensitive sensors to monitor water quality. Hence this review is focused on recent advances on synthesis strategies, and optical and chemical properties of various MNCs including their applications to develop optical assay for Hg²⁺ ions in aqueous solutions.

Sustainable chemistry approach for the preparation of bluish green emissive copper nanoclusters from Justicia adhatoda leaves extract: a facile analytical approach for the sensing of myoglobin and l-thyroxine

Sustainable chemistry approach for synthesis of fluorescent copper nanoclusters for sensing of myoglobin and l-thyroxine.

Fluorescent noble metal nanoclusters for contaminants analysis in food matrix

Recently, food safety issues caused by contaminants have aroused great public concern. The development of innovative and efficient sensing techniques for contaminants detection in food matrix is in urgent demand. As fluorescent nanomaterials, noble metal nanoclusters have attracted much attention because of their ease of synthesis, enhanced catalytic activity and biocompatibility, and most importantly, excellent photoluminescence property that provides promising analytical applications. This review comprehensively introduced the synthesis method of noble metal nanoclusters, and summarized the application of metal nanoclusters as fluorescent sensing materials in the detection of pollutants, including pesticides, heavy metal, mycotoxin, food additives, and other contaminants in food. The detection mechanism of pesticide residues mostly relies on the inhibition of natural enzymes. For heavy metals, the detection mechanism is mainly related to the interaction between metal ions and nanoclusters or ligands. It is evidenced that metal nanoclusters have great potential application in the field of food safety monitoring. Moreover, challenges and future trends of nanoclusters were discussed. We hope that this review can provide insights and directions for the application of nanoclusters in contaminants detection.

Fabrication, calibration, and preliminary testing of microcantilever-based piezoresistive sensor for BioMEMS applications

In this study, the authors demonstrate the fabrication, calibration, and testing of a piezoresistive microcantilever-based sensor for biomedical microelectromechanical system (BioMEMS) application. To use any sensor in BioMEMS application requires surface modification to capture the targeted biomolecules. The surface alteration comprises self-assembled monolayer (SAM) formation on gold (Au)/chromium (Cr) thin films. So, the Au/Cr coating is essential for most of the BioMEMS applications. The fabricated sensor uses the piezoresistive technique to capture the targeted biomolecules with the SAM/Au/Cr layer on top of the silicon dioxide layer. The stiffness (k) of the cantilever-based biosensor is a crucial design parameter for the low-pressure range and also influence the sensitivity of the microelectromechanical system-based sensor. Based on the calibration data, the average stiffness of the fabricated microcantilever with and without Au/Cr thin film is 141.39 and 70.53 mN/m, respectively, which is well below the maximum preferred range of stiffness for BioMEMS applications. The fabricated sensor is ultra-sensitive and selective towards Hg²⁺ ions in the presence of other heavy metal ions (HMIs) and good enough to achieve a lower limit of detection 0.75 ng/ml (3.73 pM/ml).

Carbon-based Nanomaterials and Curcumin: A Review of Biosensing Applications

Curcumin, the main active constituent of turmeric (Curcuma longa L.), is a naturally occurring phenolic compound with a wide variety of pharmacological activities. Although it has multiple pharmaceutical properties, its bioavailability and industrial usage are hindered due to rapid hydrolysis and low water solubility. Due to the growing market of curcumin, exact determination of curcumin in trade and human biological samples is important for monitoring therapeutic actions. Different nanomaterials have been suggested for sensing curcumin; and in this case, carbon-based nanomaterials (CNMs) are one of the most outstanding developments in nanomedicine, biosensing, and regenerative medicine. There are a considerable number of reports which have shown interesting potential of CNMs-based biosensors in the sensitive and selective detection of curcumin. Therefore, this review aims to increase understanding the interaction of curcumin with CNMs in the context of biosensing.

Dual protein ligand-modified gold nanoclusters for selective detection of serum sodium copper chlorophyllin

Precisely tuning the emission wavelength of dual ligands co-functionalized gold nanoclusters (AuNCs) presents a bright prospect for highly selective drug detection. In this study, gold nanoclusters (AuNCs) with strong red fluorescence at 633 nm were synthesized using bovine serum albumin (BSA) and bromelain (Bro) as dual ligands for highly selective detection of sodium copper chlorophyllin (SCC). Interestingly, the auto-fluorescence interference of the dual ligands was effectively avoided due to the fluorescence emission red-shifts of the prepared BSA/Bro@AuNCs; this may be mainly due to the rigid structure of the proteins. The fluorescence of BSA/Bro@AuNCs was quenched after addition of SCC, which performed well and provided a good linear calibration curve in the 5.0-25.0 μM range (R² = 0.999), and a detection limit as low as 0.5 μM. The proposed assay was further applied to the measurement of SCC in rat serums after an intravenous injection. The dual protein ligand-capped AuNCs showed great potential for drug analysis in actual biological samples.

Natural protein-templated fluorescent gold nanoclusters: Syntheses and applications

For the past decades, the synthesis of metal nanoclusters has been a great interest for research, for their unique physicochemical properties and great contributions to the catalytic, electrical and biomedical applications. Protein-templated gold nanoclusters (AuNCs) is a kind of fluorescent nanomaterials with good solubility, excellent stability, biocompatibility, decent quantum yields and active groups (-COOH, -NH₂) for facilitating modifications. Natural proteins are easily available, commercially affordable, diverse and multitudinous in animals, plants and foods, which provide a template pool for the exploration of AuNCs. This is one of the few reviews of specifically focusing on the natural protein-templated fluorescent AuNCs. The syntheses, properties and applications of different AuNCs were enumerated. Prospects were given on utilizing structure-modified proteins, bioactive enzymes, antibodies which should endow the AuNCs more favourable fluorescence performances and functional characteristics. The applications of AuNCs in analytical, biomedical and food sciences would be further heightened.

A low-cost paper-based aptasensor for simultaneous trace-level monitoring of mercury (II) and silver (I) ions

Mercury (Hg²⁺) and silver (Ag⁺) ions possess the harmful effects on public health and environment that makes it essential to develop the sensing techniques with great sensitivity for the ions. Metal ions commonly coexist in the different biological and environmental systems. Hence, it is an urgent demand to design a simple method for the simultaneous detection of metal ions, peculiarly in the case of coexisting Hg²⁺ and Ag⁺. This study introduces a low-cost paper-based aptasensor to monitor Hg²⁺ and Ag⁺, simultaneously. The strategy of the sensing array is according to the conformational changes of Hg²⁺- and Ag⁺-specific aptamers and their release from the GO surface after the injection of the target sample on the sensing platform. Through monitoring the fluorescence recovery changes against the concentrations of the ions, Hg²⁺ and Ag⁺ can be determined as low as 1.33 and 1.01 pM. The paper-based aptasensor can simultaneously detect the ions within about 10 min. The aptasensor is applied prosperously to monitor Hg²⁺ and Ag⁺ in human serum, water, and milk. The designed aptasensor with the main advantages of simplicity and feasibility holds the supreme potential to develop a cost-effective sensing method for environmental monitoring, food control, and human diagnostics.

Sensitive and selective assay of uranyl based on the aggregation induced fluorescent quenching of protamine capped gold nanoclusters

The protamine capped gold nanoclusters (AuNCs@PRT) were synthesized by an one-pot approach, and utilized as a nanoprobe for highly sensitive and selective assay of U(VI) ions. The method is based on the aggregation induced fluorescent quenching of AuNCs@PRT by U(VI) ions. Under optimum conditions, the decrease of fluorescence intensity displayed a good linear correlation with the concentration of U(VI) ions ranging from 20.4 nM to 9.74 μM, with a detection limit of 6.1 nM. The relative standard deviations were 3.86%, 1.41% and 1.71% via 11 detections at concentrations of 40 nM, 0.40 μM and 4.0 μM of U(VI), respectively. The quenching mechanism was demonstrated to be due to the binding of U(VI) towards PRT to cause the aggregation of AuNCs@PRT rather than metal-metal interaction. The results suggest the potential application of this approach for monitoring the level of U(VI) in environmental samples.

Acid Oxidation of Muskmelon Fruit for the Fabrication of Carbon Dots with Specific Emission Colors for Recognition of Hg2+ Ions and Cell Imaging

In this study, water-soluble emissive carbon dots (CDs) are effectively fabricated with specific optical properties and colors by acid oxidation of muskmelon (Cucumis melo) fruit, which are termed as C. melo CDs (CMCDs). The fluorescence properties of CMCDs were tuned by controlling the experimental conditions that allow them to emit different colors, that is, blue (B-), green (G-), and yellow (Y-) CMCDs, with different emission wavelengths at 432, 515, and 554 nm when excited at 342, 415, and 425 nm, respectively. The fabricated multicolor-emissive CDs were confirmed by various analytical techniques. The sizes of B-, G-, and Y-CMCDs were found to be ∼3.5, ∼4.3, and ∼5.8 nm, respectively. The as-prepared CMCDs display stable emissions with quantum yields of 7.07, 26.9, and 14.3% for the three CMCDs, which could act as a promising probe for the selective detection of Hg²⁺ ions. Upon the addition of Hg²⁺ ions, the fluorescence intensity of G-CMCDs at 515 nm was quenched largely than that of B- and Y-CMCDs. The spectroscopic results display that the G-CMCDs acted as a sensor for the detection of Hg²⁺ ions with a wide linear range from 1.0 to 25 μM (R ² = 0.9855) with a detection limit of 0.33 μM. This method was successfully applied to detect Hg²⁺ ions in biological and water samples. The fabricated multicolor-emissive CMCDs possess the cell (Cunninghamella elegans, Aspergillus flavus, and Rhizoctonia solani) imaging property, suggesting the biocompatible nature for multicolor imaging of various cells.

Trypsin mediated one-pot reaction for the synthesis of red fluorescent gold nanoclusters: Sensing of multiple analytes (carbidopa, dopamine, Cu2+, Co2+ and Hg2+ ions)

Herein, we fabricated fluorescent gold nanoclusters (Au NCs) by using trypsin as a ligand. The fabricated trypsin-Au NCs emit bright red color fluorescence upon the exposure of 365 nm UV light. The trypsin-Au NCs are stable and well dispersed in water, which exhibited strong red emission peak at 665 nm upon excitation wavelength of 520 nm. The red fluorescence of trypsin-Au NCs was greatly quenched by the addition of multiple analytes such as drugs (carbidopa and dopamine) and three divalent metal ions (Cu²⁺, Co²⁺ and Hg²⁺ ion). As a result, a novel fluorescence "turn-off" probe was developed for the detection of the above analytes with good selectivity and sensitivity. This method exhibits the detection limits for carbidopa, dopamine, Cu²⁺, Co²⁺ and Hg²⁺ ions are 6.5, 0.14, 5.2, 0.0078, and 0.005 nM, respectively. The trypsin-Au NCs were successfully applied to detect drugs (carbidopa, and dopamine) in pharmaceutical samples and metal ions (Cu²⁺, Co²⁺ and Hg²⁺ ion) in biofluids and water samples, exhibiting good precision and accuracy, which offers a facile analytical strategy for assaying of the above analytes in pharmaceutical and biological samples.

Easily synthesized carbon dots for determination of mercury(II) in water samples

In this work, a simple thermal method was used to synthesize carbon dots from citric acid and glycine precursors. It was found that Hg(II) ions can selectively quench the fluorescence emission of these carbon dots. Subsequently, a sensor was designed and optimized for the determination of Hg(II) ions. The limit of detection and quantification of the sensor were found to be 38 and 112 ppb, respectively. The sensor showed good selectivity toward Hg(II) ions and was successfully used for the determination of Hg(II) ions in mineral water samples.

A label-free “turn-on” fluorescence platform for glucose based on AuNCs@MnO2 nanocomposites

The principle of sensitive detection of glucose in human serum using Bro-AuNCs @MnO₂ nanocomposites as a fluorescent sensor.

Gold nanocluster-based fluorescence sensing probes for detection of dipicolinic acid

A switched-on fluorescence sensing probe for the detection of dipicolinic acid (DPA) is demonstrated in this study.

Sensitivity limits of biosensors used for the detection of metals in drinking water

Even when present in very low concentrations, certain metal ions can have significant health impacts depending on their concentration when present in drinking water. In an effort to detect and identify trace amounts of such metals, environmental monitoring has created a demand for new and improved methods that have ever-increasing sensitivities and selectivity. This paper reviews the sensitivities of over 100 recently published biosensors using various analytical techniques such as fluorescence, voltammetry, inductively coupled plasma techniques, spectrophotometry and visual colorimetric detection that display selectivity for copper, cadmium, lead, mercury and/or aluminium in aqueous solutions.