Photonic crystal enhanced gold-silver nanoclusters fluorescent sensor for Hg2+ ion

Superparamagnetic photonic crystals with DNA probes for rapid visual detection of mercury

A novel superparamagnetic photonic crystal DNA probe (Fe3O4@SiO2@amino@DNA SPC) was developed to enable rapid visual detection of Hg2+. This unique photonic crystal (PC) was synthesized by combining superparamagnetic nanospheres with DNA probes. The DNA probe, rich in thymine (T), detects mercury ions through base mismatch, resulting in the formation of T-Hg2+-T loop hairpin structures. With the binding of Hg2+ to the probe attached to superparamagnetic nanospheres, the PC structure assembled by these nanospheres, formed by the magnetic field, was changed. This change enhanced the reflection intensity; it could be quantified using a fiber optic spectrometer and was visible to the naked eye. The Fe3O4@SiO2@amino@DNA SPC, specific to Hg2+, exhibited a reflection peak at 679 nm, which intensified with increasing Hg2+ concentration. The reflection intensity increased by 132.58 a.u., and the PC color shifted from red to yellow as the Hg2+ concentration increased from 0.1 μg/L to 1 mg/L.

Excitation/emission-enhanced heterostructure photonic crystal array synergizing with "DD-A" FRET entropy-driven circuit for high-resolution and ultrasensitive analysis of ctDNA

Circulating tumor DNA (ctDNA) is an emerging biomarker of liquid biopsy for cancer. But it remains a challenge to achieve simple, sensitive and specific detection of ctDNA because of low abundance and single-base mutation. In this work, an excitation/emission-enhanced heterostructure photonic crystal (PC) array synergizing with entropy-driven circuit (EDC) was developed for high-resolution and ultrasensitive analysis of ctDNA. The donor donor-acceptor FÖrster resonance energy transfer ("DD-A" FRET) was integrated in EDC based on the introduction of simple auxiliary strand, which exhibited higher sensitivity than that of traditional EDC. The heterostructure PC array was constructed with the bilayer periodic nanostructures of nanospheres. Because the heterostructure PC has the adjustable dual photonic band gaps (PBGs) by changing nanosphere sizes, and the "DD-A" FRET can offer the excitation and emission peak with enough distance, it helps the successful matches between the dual PBGs of heterostructure PC and the excitation/emission peaks of "DD-A" FRET; thus, the fluorescence from EDC can be enhanced effectively from both of excitation and emission processes on heterostructure PC array. Besides, high-resolution of single-base mutation was obtained through the strict recognition of EDC. Benefiting from the specific spectrum-matched and synergetic amplification of heterostructure PC and EDC with "DD-A" FRET, the proposed array obtained ultrasensitive detection of ctDNA with LOD of 12.9 fM, and achieved the analysis of mutation frequency as low as 0.01%. Therefore, the proposed strategy has the advantages of simple operation, mild conditions (enzyme-free and isothermal), high-sensitivity, high-resolution and high-throughput analysis, showing potential in bioassay and clinical application.

Development of an angle-adjustable photonic crystal fluorescence platform for sensitive detection of oxytetracycline

We pioneered an angle-adjustable photonic crystal fluorescence platform (APC-Fluor) that integrates PCs, an angular resolution spectrometer and a strategically aligned laser source. This configuration, featuring a coaxial rotating swing arm, allows for precise control over the angles of incidence and emission. The presence of photonic crystal microcavities facilitates the dispersion of fluorescent materials and promotes the transition of electrons from the excited state to the lowest vibrational energy level. The optical resonance effect triggered by modulating the alignment of the reflection peaks of the photonic crystals with the emission peaks of the fluorescent materials can significantly enhance the fluorescence intensity. Compared with the single BSA-AuNCs, the optimized fluorescence intensity can be significantly increased by 11.9-fold. The APC-Fluor system showcases rapid and highly sensitive detection capabilities for oxytetracycline (OTC), exhibiting a response across a concentration range from 2 to 1 × 104 nM and achieving a notably low detection limit of 1.03 nM.

Role of silver nanoparticles and silver nanoclusters for the detection and removal of Hg(ii)

Silver metal, being a 3d transition metal in group 11 in the periodic table, is widely used in material science for its distinguished plasmonic properties. Nanoparticles (NPs) and nanoclusters (NCs) are widely used in sensing applications having a surface plasmon band and emissive properties, respectively. Mercury is one of the detrimental toxins and threats to various ecosystems. The distinction between nanoparticles and nanoclusters, the utility and toxicity of heavy metal mercury, fluorometric and colorimetric approaches to the recognition of mercury ions with NPs and NCs, the mechanism of detection, spot detection, and natural water sample analyses were illustrated in detail in this review article. Moreover, the sensing platform and analyte (Hg2+) fate were described for substantiating the mechanism. It was observed that NCs are mostly utilized for fluorometric approaches, while NPs are mostly employed for colorimetric approaches. Fluorometric detection is mainly quenching-based. However, sensing with enhancement was found in a few reports. Adulteration of other metals with silver particles often modifies the sensing platform.

A Ratiometric Fluorescent Sensor for Penicillin G Based on Color-Tunable Gold-Silver Nanoclusters

Excessive administration of penicillin G and improper disposal of its residues pose a serious risk to human health; therefore, the development of convenient methods for monitoring penicillin G levels in products is essential. Herein, novel gold-silver nanoclusters (AuAgNCs) were synthesized using chicken egg white and 6-aza-2-thiothymine as dual ligands with strong yellow fluorescence at 509 and 689 nm for the highly selective detection of penicillin G. The AuAgNCs were characterized using transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet-visible absorption spectrophotometry, and fluorescence spectrophotometry. Under optimum conditions, the fluorescence intensity decreased linearly with the concentration of penicillin G from 0.2 to 6 μM, with a low detection limit of 18 nM. Real sample analyses indicated that a sensor developed using the AuAgNCs could detect penicillin G in urine and water samples within 10 min, with the recoveries ranging from 99.7 to 104.0%. The particle size of the AuAgNCs increased from 1.80 to 9.06 nm in the presence of penicillin G. We believe the aggregation-induced quenching of the fluorescence of the AuAgNCs was the main mechanism for the detection of penicillin G. These results demonstrate the ability of our sensor for monitoring penicillin G levels in environmental and clinic samples.

Recent advances in fluorescent materials for mercury(ii) ion detection

Invading mercury would cause many serious health hazards such as kidney damage, genetic freak, and nerve injury to human body. Thus, developing highly efficient and convenient mercury detection methods is of great significance for environmental governance and protection of public health. Motivated by this problem, various testing technologies for detecting trace mercury in the environment, food, medicines or daily chemicals have been developed. Among them, the fluorescence sensing technology is a sensitive and efficient detection method for detecting Hg2+ ions due to its simple operation, rapid response and economic value. This review aims to discuss the recent advances in fluorescent materials for Hg2+ ion detection. We reviewed the Hg2+ sensing materials and divided them into seven categories according to the sensing mechanism: static quenching, photoinduced electron transfer, intramolecular charge transfer, aggregation-induced emission, metallophilic interaction, mercury-induced reactions and ligand-to-metal energy transfer. The challenges and prospects of fluorescent Hg2+ ion probes are briefly presented. We hope that this review can provide some new insights and guidance for the design and development of novel fluorescent Hg2+ ion probes to promote their applications.

Colloidal Photonic Crystal-Enhanced Fluorescence of Gold Nanoclusters: A Highly Sensitive Solid-state Fluorescent Probe for Creatinine

Gold nanoclusters (AuNCs) are an intensely pursued class of fluorophores with excellent biocompatibility, high water solubility, and ease of further conjugation. However, their low quantum yield limits their applications, such as ultra-sensitive chemical or molecular sensing. To address this problem, various strategies have been adopted for augmenting their fluorescence intensity. Herein, we report a facile and scalable approach for the fluorescence enhancement of bovine serum albumin (BSA) capped AuNCs (BSA-AuNCs) using periodic, close-packed polystyrene colloidal photonic crystals (CPCs). The slow photon effect at the bandgap edges is utilized for the increased light-matter interactions and thereby enhancing the fluorescence intensity of the BSA-AuNCs. Compared to the planar polystyrene control sample, the CPC film yielded a 14-fold enhancement in fluorescence intensity. Further, we demonstrated the as-prepared BSA-AuNCs-CPC as a solid-state platform for the highly sensitive and selective fluorescence turn-off detection of creatinine at nanomolar level.

A "turn-on" inverse opal photonic crystal fluorescent sensing film for detection of cysteine and its bioimaging of living cells

A "turn-on" inverse opal photonic crystal fluorescent sensing film infiltrated with a coumarin derivative is reported for the reliable and accurate detection of cysteine in human serum and fluorescence imaging of living cells. The coumarin derivative containing allyl ester specifically reacts with cysteine by ammonolysis to generate a fluorescent product whose emission wavelength is at ~ 535 nm, providing a selective fluorescence detection for cysteine. The emitted fluorescence is significantly enhanced due to the slow photon effect derived from the photonic crystal film. This is because the emission wavelength is overlapped with the blue-band edge of the photonic stopband of the selected inverse opal film. The fluorescence enhancement effect endows the prepared inverse opal film with highly sensitive detection with a limit of detection of 3.23 × 10^-9 mol/L and a wide linear detection range of 1 × 10^-7 - 1 × 10^-3 mol/L. A fast response within 30 s toward cysteine is also achieved due to the three-dimensional interconnected macroporous structure with a high-specific surface area of the inverse opal film. The prepared inverse opal fluorescent sensing film has been successfully applied to the detection of cysteine in human serum and bioimaging of living cells. In the diluted human serum, the recoveries for the detection of cysteine were 97.92 - 107.20%, and the relative standard deviations were 2.61-9.04%, demonstrating the potential applicability of the inverse opal fluorescent sensing film to real sample analysis. The method may provide a universal strategy for constructing various photonic crystal fluorescent sensing films by using different fluorescent probes.

Advances in functional photonic crystal materials for the analysis of chemical hazards in food

Chemical contaminants in food generally include natural toxins (mycotoxins, animal toxins, and phytotoxins), pesticides, veterinary drugs, environmental pollutants, heavy metals, and illegal additives. Developing a low-cost, simple, and rapid detection technology for harmful substances in food is urgently needed. Analytical methods based on different advanced materials have been developed into rapid detection methods for food samples. In particular, photonic crystal (PC) materials have a unique surface periodic structure, structural color, a large surface area, easy integration with photoelectronic and magnetic devices which have great advantages in the development of rapid, low-cost, and highly sensitive analytical methods. This review focuses on the PC materials in the view of their fabrication processes, functionalized recognition components for the specific recognition of hazardous substances, and applications in the separation, enrichment, and detection of chemical hazards in real samples. Suspension array based on three-dimensional PC microspheres by droplet-based microfluidic assembly is a great promising and powerful platform for food safety detection fields. For the PCs selective analysis, biological antibodies, aptamers, and molecularly imprinted polymers (MIPs) could be modified for specific recognition of target substances, particularly MIPs because of their low-cost and easy mass production. Based on these functional PCs, various toxic and hazardous substances can be selectively enriched or recognized in real samples and further quantified in combination of liquid chromatography method or optical detection methods including fluorescence, chemiluminescence, and Raman spectroscopy.

The recognition of aristolochic acid I based on fluorescence quenching of bovine serum albumin-stabilized gold nanoclusters

Aristolochic acid I (AAI) is one of the nephrotoxic derivatives present in genera Aristolochia and Asarum. Although some detection strategies for monitoring AAI have been reported, the application of these methods is limited because they involve tedious preparation and require professional operation. In this work, bovine serum albumin (BSA) has been introduced as a reducing agent and stabilizing agent to synthesize gold nanoclusters with strong red fluorescence for the rapid and effective detection of AAI. Under excitation at 328 nm, the fluorescence intensity at the maximum emission wavelength of the bovine serum albumin-stabilized gold nanoclusters (BSA-AuNCs) decreased with the addition of AAI, and the degree of quenching showed a linear relationship with the concentration of AAI from 0.1-12.8 μg mL^-1. The obtained BSA-AuNCs were stable, and quenching in the presence of AAI could be achieved within 10 seconds. Here, we have focused on the application of these gold nanoclusters as an optical sensing material for AAI in rat urine samples, including a discussion on the detection mechanism. The detection result of the fluorescent probe was consistent with that of the HPLC method. In view of this reality, the reported protein-AuNCs sensing platform can serve as a convenient detection strategy in toxicological analyses.

Surface engineered bimetallic gold/silver nanoclusters for in situ imaging of mercury ions in living organisms

Chemical sensing for the sensitive and reliable detection of mercury(II) ions (Hg²⁺) is of great importance in environmental protection, food safety, and biomedical applications. Due to the bio-enrichment property of Hg²⁺ in organisms, it is particularly meaningful to develop an effective tool that can in situ and rapidly monitor the level of Hg²⁺ in living organisms. In this work, we report ligand functionalized gold-silver bimetallic nanoclusters with bright red fluorescence as intracellular probes for imaging Hg²⁺ in living cells and zebrafish. The bimetallic nanoclusters of DTT-GSH@Au/AgNCs (DG-Au/AgNCs) with strong fluorescence that benefited from the synergistic effect of Au and Ag atoms were obtained through a one-pot synthesis method, incorporating glutathione (GSH) and dithiothreitol (DTT) as the reducers and functionalized ligands. Attractively, the bright red fluorescence of DG-Au/AgNCs could be rapidly and selectively quenched by Hg²⁺ within 1 min with a very low detection limit of 1.01 nM. Additionally, DG-Au/AgNCs had a great advantage in the detection of Hg²⁺ in living cells and zebrafish owing to its notably strong red fluorescence at 665 nm, which could avoid effectively auto-fluorescence interference from the organism. Such easily prepared bimetallic fluorescent nanoclusters would be expected to provide a noninvasive and sensitive approach in the detection of heavy metals in situ for environmental protection.

Recent Trends and Future Perspectives of Emergent Analytical Techniques for Mercury Sensing in Aquatic Environments

Environmental emissions of mercury from industrial waste and natural sources, even in trace amounts, are toxic to organisms and ecosystems. However, industrial-scale mercury detection is limited by the high cost, low sensitivity/specificity, and poor selectivity of the available analytical tools. This review summarizes the key sensors for mercury detection in aqueous environments: colorimetric-, electrochemical-, fluorescence-, and surface-enhanced Raman spectroscopy-based sensors reported between 2014-2021. It then compares the performances of these sensors in the determination of inorganic mercury (Hg²⁺ ) and methyl mercury (CH₃ Hg⁺ ) species in aqueous samples. Mercury sensors for aquatic applications still face serious challenges in terms of difficult deployment in remote areas and low robustness, reliability, and selectivity in harsh environments. We provide future perspectives on the selective detection of organomercury species, which are especially toxic and reactive in aquatic environments. This review is intended as a valuable resource for scientists in the field of mercury sensing.

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.

A visualized ratiometric fluorescence sensing system for copper ions based on gold nanoclusters/perovskite quantum dot@SiO2 nanocomposites

Excessive copper ions (Cu²⁺) cause serious environmental pollution and even endanger the health of organisms. Fluorescence chemosensing materials are widely used in the detection of metal ions due to their simple operation and high sensitivity. In this study, SiO₂-encapsulated single perovskite quantum dot (PQD@SiO₂) core-shell nanostructures which show strong, stable, and green fluorescence are synthesized and composited with gold nanoclusters (AuNCs) which show Cu²⁺-sensitive and red light-emitting fluorescence to obtain a visualized ratiometric fluorescence sensor (AuNCs/PQD@SiO₂) for the detection of Cu²⁺. In the visualized detection of Cu²⁺, the green fluorescence emitted from the ion-insensitive PQD@SiO₂ component is used as a reference signal and the red fluorescence emitted by ion-sensitive AuNC component is adopted as a sensing signal. In the presence of Cu²⁺, the red fluorescence is quenched whereas the green fluorescence remains stable, which results in a visualized fluorescence color change from orange-red to yellow and finally to green with increasing Cu²⁺ concentration. The significant change in the fluorescence color of AuNCs/PQD@SiO₂ in response to Cu²⁺ enables a rapid, sensitive, and visualized detection of Cu²⁺. Further accurate and sensitive ratiometric fluorescence analysis of Cu²⁺ can be accomplished by measuring the ratio of fluorescence intensities at 643 and 520 nm (I₆₄₃/I₅₂₀) at a certain Cu²⁺ level. The developed AuNCs/PQD@SiO₂-based sensor has been validated by its satisfactory application in the detection of Cu²⁺ in human serum and environmental water samples.

Fluorine-free synthesis of Ti3C2 MQDs for smartphone-based fluorescent and colorimetric determination of acetylcholinesterase and organophosphorus pesticides

Ti₃C₂ MQDs were synthesized using an effective fluorine-free method with excitation/emission maxima at 390/490 nm and a fluorescence quantum yield of 11.78%. In contrast to the traditional, hazardous, and time-consuming process of HF pretreatment, our fluorine-free method is safe and simple. Acetylcholinesterase (AChE) could catalyze the hydrolysis of acetylthiocholine (ATCh) to produce thiocholine which was further reacted with Ehrman's reagent and decomposed to form a yellow product 2-nitro-5-thiobenate anion (TNB). Due to the obvious overlap between the excitation spectrum of Ti₃C₂ MQDs and the absorption spectrum of TNB, AChE catalyzed the hydrolysis of substrate DTNB/ATCh to form TNB, which can effectively quench the fluorescence of Ti₃C₂ MQDs through the inner filter effect (IFE). However, the presence of organophosphorus (OPs) inhibited the activity of AChE, leading to a less expressed IFE and increasing recovery of fluorescence. This was used for the quantification of OPs with a detection limit of 0.20 μg·L^-1. Moreover, with the constant increase of AChE activity, the color of the reaction system changed visibly from colorless to yellow, and then from yellow to colorless with further continuous addition of OPs. A colorimetric detection with a paper-based sensor of AChE activity and OP concentration was also fabricated by analyzing changes in RGB value using a smartphone APP. In this work, we proposed an effective fluorescence/colorimetric two-mode detection method, which opened a new horizon to detect other targets.

Persistent luminescence nanorods-based autofluorescence-free biosensor for prostate-specific antigen detection

Persistent luminescent nanoparticles (PLNPs) are a class of materials with excellent optical properties, which can continue to emit light for a long time after removing the excitation light source. This feature enables PLNPs to be used for development of biological detection modes without autofluorescence background. In this study, we prepared Zn₂GeO₄: Mn²⁺, Pr³⁺ (ZGOMP) nanorods through a one-pot hydrothermal method. Using the pH-responsive luminescence behavior of ZGOMP, we developed an autofluorescence-free biosensor using ZGOMP as a probe and gluconic acid as a quencher to detect prostate-specific antigen (PSA). Hybridization chain reaction (HCR) and magnetic separation system were introduced in the design to achieve efficient signal amplification. Under the optimal conditions, the as-designed autofluorescence-free sensing platform showed high selectivity, and showed a good luminescence response to PSA within the linear range of 0.001-10 ng/mL at a detection limit of 0.64 pg/mL. The excellent analytical performance shows that the current strategy provides an effective platform for clinical sample analysis.

Copper nanoclusters with/without salicylaldehyde-modulation for multifunctional detection of mercury, cobalt, nitrite and cyanide ions in aqueous solution and bioimaging

The sensitive determination of multiple heavy metal ions and toxic anions is important in biological and environmental fields. Here we report a facile strategy to construct a multifunctional chemosensor for the detection of Hg²⁺, [Formula: see text]Co²⁺, and CN^- in aqueous solution based on the fluorescent copper nanoclusters (Cu NCs). It was interesting to find that salicylaldehyde (SA) could effectively modulate the fluorescence property and sensing behavior of Cu NCs. In the absence of SA, Cu NCs showed 'on-off' fluorescence responses at the addition of Hg²⁺ and [Formula: see text] under different quenching mechanisms. Upon the presence of SA, Cu NCs exhibited a strong intramolecular charge transfer emission at 500 nm, accompanied by the decrease of the initial fluorescence of Cu NCs at 430 nm. This fluorescence on-state of Cu NC-SA at 500 nm was found to be exclusively turned off by Co²⁺ and enhanced by CN^-. Spectroscopy results combined with thermodynamic analysis provided sufficient information to deduce the sensing mechanisms. Finally, the Cu NCs showed high biocompatibility and were able to be used for fluorescence bioimaging in living cells. This study provided a novel and simple strategy to construct the multifunctional chemosensors for bioanalytical applications.

Fluorescence Sensing of Formaldehyde and Acetaldehyde Based on Responsive Inverse Opal Photonic Crystals: A Multiple-Application Detection Platform

Formaldehyde (FA) and acetaldehyde (AcH) used as common chemicals in many fields are carcinogenic. The presently reported detection methods usually need expensive instruments, professional technicians, and time-consuming processes, and the detection sensitivity still needs further improvement. Herein, we report a highly effective fluorescence (FL) sensing film for FA and AcH based on naphthalimide derivative-infiltrated responsive SiO₂ inverse opal photonic crystals (PCs), establishing a practically multiple-application detection platform for FA and AcH in air, aquatic products, and living cells. Nucleophilic addition products between the amine group of the naphthalimide derivative and aldehydes emit strong FL at ∼550 nm, realizing selective FL detection for FA and AcH. The emitted FL can be enhanced remarkably because of the slow photon effect of PCs, in which the FL wavelength is located at the stopband edge of PCs. A highly sensitive detection for FA and AcH with limits of detection of 10.6 and 7.3 nM, respectively, is achieved, increasing 3 orders of magnitude compared with that in the solution system. Additionally, the interconnected three-dimensional microporous inverse opal structure endows the sensor with a rapid response within 1 min. Furthermore, the as-prepared PC sensor can be reused by simple washing in an acidic aqueous solution. The sensing system can be used as a FL multi-detection platform for FA and AcH in air, aqueous solution, and living cells. This FL sensing approach based on small organic molecule-functionalized PCs is universally available to develop various sensors for target analytes by designing new functional organic compounds.

Optical Devices Constructed From Responsive Microgels for Polyphenols Detection

Polyphenols are used as antioxidants in various foods and beverages, which are considered to be a health benefit. The measurement of polyphenols contents is of great interest in food chemistry and health science. This work reported a microgels based photonic device (etalon) to detect polyphenols. Dopamine was used as a model compound of polyphenols. Herein, we proposed a “block” concept for dopamine detection. The dopamine was oxidized and formed dopamine films catalyzed by tyrosinase on the surface of etalon. As the etalon was immersed in ZnCl₂, the dopamine films blocked the ZnCl₂ diffusion into etalon that caused optical property changes. The film thickness is associated with the concentration of dopamine which can be readout via optical signals.

Photonic Crystal of Polystyrene Nanomembrane: Signal Amplification and Low Triggered Potential Electrochemiluminescence for Tetracycline Detection

In this work, a low triggered potential electrochemiluminescence strategy based on gold-filled photonic crystals (GPCs) electrodes composed of photonic crystals self-assembled with polystyrene spheres and gold nanoparticles embedded in the gaps of the photonic crystals was proposed. The GPCs electrodes served as the detection platform to bind antigen, and Ru(bpy)₃²⁺-COOH as a luminophore was labeled on the antibody (Ab). Then, Ru(bpy)₃²⁺-COOH/Ab was connected to the immobilized antigen on the surface of the photonic crystals by the immunoreaction to avoid direct contact with the gold nanoparticles surface. ECL emission can only be initiated by electrochemical oxidation of tripropylamine (TPrA) since Ru(bpy)₃²⁺-COOH cannot be oxidized directly on the electrode surface. The TPrA^·+ and TPrA^· radicals generated by the oxidation of TPrA can spread to the vicinity of Ru(bpy)₃²⁺-COOH over a short distance and react with the Ru(bpy)₃²⁺-COOH, eventually producing ECL emission. The potential of ECL emission caused by TPrA oxidation was about 300 mV lower than that caused by Ru(bpy)₃²⁺-COOH oxidation because the oxidation potential of TPrA (0.95 V vs SCE) was lower than Ru(bpy)₃²⁺-COOH (1.25 V vs SCE). Furthermore, the photonic crystals nanomembrane has the capability to enhance electrochemiluminescence. Thereafter, tetracycline antibiotic as a model compound was successfully detected via competitive immunoassay on GPCs electrodes with a detection limit of 0.075 pg/mL (S/N = 3), which has broad application prospects in the field of analysis and detection.

"Turn-off" sensing probe based on fluorescent gold nanoclusters for the sensitive detection of hemin

Balanced level of hemin in the body is fundamentally important for normal human organ function. Therefore, environmentally benign, stable, and fluorescent metal nanoclusters (NCs) for selective and sensitive detection of hemin have been investigated and reported. Herein, highly orange red emissive gold NCs are successfully synthesized using glutathione as a reducing and stabilizing agent (GSH-Au NCs). The clusters are characterized using various techniques like Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), UV-vis spectroscopy, and fluorescence spectrometer. The fluorescence intensity of as-synthesized Au NCs strongly quenched upon addition of different concentrations of hemin. The decrease in fluorescence intensity of GSH-Au NCs has been applied for determination of hemin concentration in the linear range from 1 to 25 nM with a low limit of detection (LOD) of 0.43 nM. The method was also successfully applied for quantification of hemin in human serum sample. In view of this reality, the system can be considered as a possible strategy and excellent platform for determination of hemin in various areas of application.

Ratiometric sensors with selective fluorescence enhancement effects based on photonic crystals for the determination of acetylcholinesterase and its inhibitor

Ratiometric fluorescent sensors are powerful tools for quantitative analyses.