Engineered Electrochemiluminescence Biosensors for Monitoring Heavy Metal Ions: Current Status and Prospects

Metal ion contamination has serious impacts on environmental and biological health, so it is crucial to effectively monitor the levels of these metal ions. With the continuous progression of optoelectronic nanotechnology and biometrics, the emerging electrochemiluminescence (ECL) biosensing technology has not only proven its simplicity, but also showcased its utility and remarkable sensitivity in engineered monitoring of residual heavy metal contaminants. This comprehensive review begins by introducing the composition, advantages, and detection principles of ECL biosensors, and delving into the engineered aspects. Furthermore, it explores two signal amplification methods: biometric element-based strategies (e.g., HCR, RCA, EDC, and CRISPR/Cas) and nanomaterial (NM)-based amplification, including quantum dots, metal nanoclusters, carbon-based nanomaterials, and porous nanomaterials. Ultimately, this review envisions future research trends and engineered technological enhancements of ECL biosensors to meet the surging demand for metal ion monitoring.

Cell-free arsenic biosensors with applied nanomaterials: critical analysis

Arsenic is a ubiquitously found metalloid in our ecosystem because of natural and anthropogenic activities. People exposed to a higher level of arsenic become susceptible to several disorders, including cancer. According to current statistics, the population chronically exposed to arsenic has surpassed 200 million. Therefore, its detection in our environment is of great importance. There are many analytical techniques for the assessment of arsenic in different kinds of environmental samples. Among these techniques, the biosensor is considered a convenient platform and a widely applied analytical device for rapid qualitative and quantitative analysis in the field of environmental monitoring, food safety, and disease diagnosis. Today, there is a trend of including nanomaterials in sensors and biosensors because it empowers researchers to explore new arsenic detection methods and to enhance their analytical capabilities. In this review article, we summarized the latest developments in arsenic biosensors in particular with emphasis on the works based on cell-free approaches that are protein/enzyme-based, DNA-based, and aptamer-based utilizing various transduction platforms. In the meantime, we compared the capabilities that were related to these cell-free arsenic biosensors. This review article also highlights the development and application of novel nanomaterials for arsenic detection.

A rapid and label-free DNA-based interference reduction nucleic acid amplification strategy for viral RNA detection

Common reference methods for COVID-19 diagnosis include thermal cycling amplification (e.g. RT-PCR) and isothermal amplification methods (e.g. LAMP and RPA). However, they may not be suitable for direct detection in environmental and biological samples due to background signal interference. Here, we report a rapid and label-free interference reduction nucleic acid amplification strategy (IR-NAAS) that exploits the advantages of luminescent iridium(III) probes, time-resolved emission spectroscopy (TRES) and multi-branch rolling circle amplification (mbRCA). Using IR-NAAS, we established a luminescence approach for diagnosing COVID-19 RNAs sequences RdRp, ORF1ab and N with a linear range of 0.06-6.0 × 10⁵ copies/mL and a detection limit of down to 7.3 × 10⁴ copies/mL. Moreover, the developed method was successfully applied to detect COVID-19 RNA sequences from various environmental and biological samples, such as domestic sewage, and mice urine, blood, feces, lung tissue, throat and nasal secretions. Apart from COVID-19 diagnosis, IR-NAAS was also demonstrated for detecting other RNA viruses, such as H1N1 and CVA10, indicating that this approach has great potential approach for routine preliminary viral detection.

c-Myc G-quadruplex is sensitively and specifically recognized by a fluorescent probe

The G-quadruplex structure formed by the c-myc gene sequence has attracted much attention due to its important physiological function in biology and wide application in nanotechnology. So far, probes capable of recognition of c-myc G-quadruplex with both high specificity and sensitivity are still scarce. This work presented a cyanine dye fluorescent probe named Cy-1, which has almost no fluorescence in aqueous solution, but showing more than 1000-fold fluorescence enhancement for recognizing c-myc G-quadruplex. Cy-1 also has good specificity and can selectively recognize c-myc G-quadruplex from other a variety of G-quadruplex and non-G-quadruplex structures. These properties make Cy-1 a promising probe for c-myc G-quadruplex recognition in nanotechnology or biology.

Ratiometric-enhanced G-Quadruplex Probes for Amplified and Mix-to-Read Detection of Mercury Pollution in Aquatic Products

Mercury, as a global toxic pollutant, is easy to be accumulated in aquatic products and poses a great threat to human health. In this work, we proposed a mix-to-read, label-free, and robust assay for detecting mercury pollution in aquatic products by engineering a ratiometric-enhanced G-quadruplex probe. The transformation from the G-quadruplex to a hairpin-like structure allows us to confer a ratiometric and leveraged response to Hg²⁺, amplifying the signal-to-background ratio for Hg²⁺ detection. Hg²⁺ response was further improved by screening parallel- and antiparallel-, single-, and multiple-stranded G-quadruplex structures. Compared to the common aptamer probes, the ratiometric-enhanced G-quadruplex probe increased the sensitivity for Hg²⁺ detection by 4.7 times. This proposed sensing system allowed a simple and one-tube homogenous detection of Hg²⁺ at room temperature using a single unlabeled DNA sequence. Its application for Hg²⁺ detection in fish and shrimp conferred satisfactory recovery rates ranging from 98.5 to 105.9%. The label-free and mix-to-read assay is promising for the onsite detection of mercury pollution and facilitating food safety of aquatic products.

Recent Progress and Development of G-Quadruplex-Based Luminescent Assays for Ochratoxin A Detection

Ochratoxin A (OTA) is a mycotoxin that is widespread throughout the world. It contaminates foods such as vegetables, fruits, and rice. It harms human health and has potential carcinogenic effects. The G-quadruplex (G4) is a tetraplexed DNA structure generated from guanine-rich DNA that has found emerging use in aptamer-based sensing systems. This review outlines the status of OTA contamination and conventional detection methods for OTA. Various G4-based methods to detect OTA developed in recent years are summarized along with their advantages and disadvantages compared to existing approaches.

One Terminal Guanosine Flip of Intramolecular Parallel G-Quadruplex: Catalytic Enhancement of G-Quadruplex/Hemin DNAzymes

Numerous studies have shown compelling evidence that incorporation of an inversion of polarity site (IPS) in G-rich sequences can affect the topological and structural characteristics of G-quadruplexes (G4s). Herein, the influence of IPS on the formation of a previously studied intramolecular parallel G4 of d(G₃ TG₃ TG₃ TG₃ ) (TTT) and its stacked higher-order structures is explored. Insertion of 3'-3' or 5'-5' IPS did not change the parallel folding pattern of TTT. However, both the species and position of the IPS in TTT have a significant impact on the G4 stability and end-stacking through the alteration of G4-G4 interfaces properties. The data demonstrate that one base flip in each terminal G-tetrad can stabilize parallel G4s and facilitate intermolecular packing of monomeric G4s. Such modifications can also enhance the fluorescence and enzymatic performances by promoting interactions between parallel G4s with N-methyl mesoporphyrin IX (NMM) and hemin, respectively.

Human telomere double G-quadruplex recognition by berberine-bisquinolinium imaging conjugates in vitro and cells

Molecular tools of double or multimeric G-quadruplexes have been given higher requirements on detection sensitivity, thermal stabilization and cell imaging to establish functions of these G-quadruplex aggregates and biological mechanisms as anticancer reagents. Here, two smart berberine-bisquinolinium conjugates (Ber-360A and Ber-PDS) by linking the berberine fluorophore ligand and an established G-quadruplex binder (i.e. bisquinolinium scaffold), have been designed and evaluated their activities and mechanisms for G-quadruplex aggregation. Two conjugates, especially Ber-PDS, are two highly selective, sensitive and fluorescent sensors which can distinguish human telomere double G-quadruplexes from other type G-quadruplexes and ds DNA. These two ligands could be the first example to stack two adjacent G-quadruplex units and fluorescently recognize human telomere double G-quadruplexes. Furthermore, conjugate Ber-PDS could enter the nucleoli and target G-quadruplex DNA through microscopy experiments, and also display strong telomerase inhibition and antitumor activities.

Construction of Time-Resolved Luminescence Nanoprobe and Its Application in As(III) Detection

As(III) is a toxic heavy metal which causes serious health problems. Therefore, the development of highly sensitive sensors for As(III) detection is of great significance. Herein, a turn-on luminescence resonance energy transfer (LRET) method based on luminous nanorods was designed for As(III) detection. Biotin-labelled As(III) aptamers were tagged to avidin functionalized luminous nanorods as energy donors, while graphene oxide (GO) acted as the energy acceptor. The adsorption of single-stranded DNA on graphene oxide resulted in the efficient quenching of the luminescence of the nanorods through the LRET process. In the presence of As(III), aptamers bonded to As(III) preferentially and resulted in the formation of aptamer-As(III) complexes. The aptamer-As(III) complexes were rubbed off from the GO surface due to their conformational change, which led to the recovery of the luminescence of the nanorods. A good linear relationship between the luminescence intensity and concentration of As(III) was obtained in the range from 1 to 50 ng·mL⁻¹, with a detection limit of 0.5 ng·mL⁻¹. Furthermore, the developed sensors showed good specificity towards As(III) and proved capable of detecting As(III) in the environment and food samples. The proposed time-resolved sensors provide a promising sensing strategy for the rapid and sensitive detection of As(III).

Conformational rearrangements of G-quadruplex topology promoted by Cu(II) 12-MCCu(II)PyrAcHA-4 metallacrown

Cu(II) 12-MC_{Cu(II)PyrAcHA}-4 metallacrown was studied by several spectroscopic techniques as an interacting ligand with G-quadruplex DNA structures. Investigations were performed on oligonucleotides bearing human telomeric and protooncogenic c-myc sequences in buffered solution mimicking ionic conditions in cellular environment. The planar square-based Cu(II) 12-MC-4 metallacrown interacts with GQ via an end-stacking mode with 1:1 stoichiometry. Circular dichroism (CD) titration revealed capability of this metallacrown to induce transformation of the GQ hybrid topology into the parallel form. Thermal melting experiment indicated higher thermal stability of both antiparallel (ΔT_m = +15 °C) and parallel (ΔT_m = ≥27 °C) G-quadruplexes in the presence of Cu (II) 12-MC-4. Indirect GQ FID assay let to determine high binding affinity of the Cu(II) 12-MC-4 to antiparallel 22Htel/Na⁺ GQ (K_MC = 3.9 (±0.4) x 10⁶ M^-1). Comparing with lower binding constants previously reported for Ln (III) 15-MC-5 and Sm (III) 12-MC-4, one can conclude that the square planar geometry and the positive charge of metallacrown play an important role in MC/GQ interactions.

Shedding light on the interaction of polydatin and resveratrol with G-quadruplex and duplex DNA: a biophysical, computational and biological approach

Among polyphenols, trans-resveratrol (tRES) and trans-polydatin (tPD) exert multiple biological effects, particularly antioxidant and antiproliferative. In this work, we have investigated the interaction of tPD with three cancer-related DNA sequences able to form G-quadruplex (G4) structures, as well as with a model duplex, and compared its behaviour with tRES. Interestingly, fluorescence analysis evidenced the ability of tPD to bind all the studied DNA systems, similarly to tRES, with tRES displaying a higher ability to discriminate G4 over duplex with respect to tPD. However, neither tRES nor tPD produced significant conformational changes of the analyzed DNA upon binding, as determined by CD-titration analysis. Computational analysis and biological data confirmed the biophysical results: indeed, molecular docking evidenced the stronger interaction of tRES with the promoter of c-myc oncogene, and immunoblotting assays revealed a reduction of c-myc expression, more effective for tRES than tPD. Furthermore, in vitro assays on melanoma cells proved that tPD was able to significantly reduce telomerase activity, and inhibit cell proliferation, with tRES producing higher effects than tPD.

Nanomaterial-based aptamer sensors for arsenic detection

Arsenic (As) is a highly toxic contaminant in the environment and a serious carcinogen for the human being. The toxicity of arsenic significantly threatens environmental and human health. The effective removing technology for arsenic remains challenging, and one of the reasons is due to the lack of powerful detection method in the complex environmental matrix. There is thus an urgent need to develop novel analytical methods for arsenic, preferably with the potential for the field-testing. To combat arsenic pollution and maintain a healthy environment and eco-system, many analytical methods have been developed for arsenic detection in various samples. Among these strategies, biosensors hold great promise for rapid detection of arsenic, in particular, nanomaterials-based aptamer sensors have attracted significant attention due to their simplicity, high sensitivity and rapidness. In this paper, we reviewed the recent development and applications of aptamer sensors (aptasensors) based-on nanomaterial for arsenic detection, in particular with emphasis on the works using optical and electrochemical technologies. We also discussed the recent novel technology in aptasensors development for arsenic detection, including nucleic acid amplification for signal enhancement and device integration for the portability of arsenic sensors. We are hoping this review could inspire further researches in developing novel nanotechnologies based aptasensors for possible on-site detection of arsenic.

Targeting G-Rich DNA Structures with Photoreactive Bis-Cyclometallated Iridium(III) Complexes

The synthesis and characterisation of three novel iridium(III) bis-cyclometallated complexes is reported. Their photophysics have been fully characterised by classical methods and revealed charge-transfer (CT) and ligand-centred (LC) transitions. Their ability to selectively interact with G-quadruplex telomeric DNA over duplex DNA has been studied by circular dichroism (CD), bio-layer interferometry (BLI) and surface plasmon resonance (SPR) analyses. Interestingly, one of the complexes was able to promote photoinduced electron transfer (PET) with the guanine DNA base, which in turn led to oxidative damage (such as the formation of 8-oxoguanine) to the telomeric sequence. To the best of our knowledge, this is the first study of highly photo-oxidising bis-cyclometallated iridium(III) complexes with G-quadruplex telomeric DNA.

Sequence Dynamics of Pre-mRNA G-Quadruplexes in Plants

Intramolecular G-quadruplexes (G4s) are secondary structures that may form within G-rich stretches of nucleic acids. Although their presence has been associated with genomic instability and mutagenicity, recent reports suggest their involvement in regulation of diverse cellular events, including transcription and translation. The majority of data regarding G4s stems from mammalian and yeast studies, leaving the plant G4s almost unexplored. Using the publicly available Arabidopsis thaliana and Oryza sativa WGS data, we examined the single nucleotide variability of sequences predicted to form G4s (pG4s) structures. We focused our analysis on protein coding transcripts and compared the results to well-characterized Homo sapiens data. We demonstrate that the overall high variability of pG4s is not uniform and differs between gene structural elements. Specifically, plant AUG-containing pG4s, located within 5'UTR/CDS junctions, are abundant and appear not to be affected by a higher frequency of sequence change, indicating their functional relevance. Furthermore, we show that substitutions lowering the probability of G4s' formation are preferred over neutral or stabilizing modifications.

Piezoelectric arsenite aptasensor based on the use of a self-assembled mercaptoethylamine monolayer and gold nanoparticles

The authors describe a piezoelectric aptasensor for arsenite. A self assembeled monolayer (SAM) of mercaptoethylamine was prepared to immobilize arsenite on the surface of a quartz crystal microbalance. Gold nanoparticles were modified with arsenite aptamer to amplify the response frequency of the biosensor. Arsenite first binds to the SAM on the gold surface of the QCM. On addition of gold nanoparticles with aptamer (DNA-AuNp), the SAM-As(III)-aptamer sandwich is formed. This increases the resonance frequency of the sensor and allows trace concentration of arsenite to be determined. The aptasensor can detect arsenite in the 8 to 1000 nmol·L^-1 concentration range with a 4.4 nmol·L^-1 lower detection limit (at S/N = 3). The sandwich structure improves the specificity of the aptasensor without considering the conformational transition of the aptamer. The strategy described here conceivably has a large potential as it shows that small molecules can be sensed by using aptamers with unknown working mechanism. Graphical abstract Schematic presentation of a piezoelectric biosensor for arsenite detection by using a mercaptoethylamine monolayer and gold nanoparticles with respect to Arsenite first binds to the SAM on the gold surface of the QCM. Next, gold nanoparticles with aptamer (DNA-AuNp) are added to form a SAM-As(III)-aptamer sandwich which affects the resonance frequency.

Label-free and sensitive detection assay for terminal deoxynucleotidyl transferase via polyadenosine-coralyne fluorescence enhancement strategy

Terminal deoxynucleotidyl transferase (TdT) is a unique template-free polymerase that randomly adds multiple deoxyribonucleoside triphosphates (dNTPs) to the 3'-OH terminus of ssDNA. This characteristic makes TdT a versatile enzymatic tool in many fields. Moreover, aberrant TdT expression is a well-recognized biomarker of several leukemic diseases and is related to carcinogenesis. In this study, we developed a facile, rapid, label-free, and convenient assay for TdT detection. TdT-generated poly A tails formed a fluorescent enhancement complex in the presence of coralyne. To achieve a better signal-to-noise ratio, we used potassium thiocyanate (KSCN), instead of other halogen anions (KCl, KBr, KI, NaI) as the quenching agent of dissociate coralyne. Our results demonstrate that this assay is extremely facile, rapid, and label-free; at levels as low as 0.025 U/mL, TdT was distinctly detected within 55 min. And the determination of TdT activity in RBL-2H3 and Reh cells lysates exhibited a good sensing performance, demonstrating its potential applications in biochemical research and clinical diagnosis.

A cyclometalated iridium(III) complex-based fluorescence probe for hypochlorite detection and its application by test strips

A new cyclometalated iridium(III) complex-based fluorescence probe (IrCN) for hypochlorite (ClO^-) has been synthesized and characterized. The probe displayed nonfluorescent around 577 nm, while a 54-fold enhancement in fluorescence emission intensity was observed after the addition of ClO^- due to the removal of C=N isomerization effect. Such "turn-on" fluorescence probe worked excellently in wide pH range (5-12) with short response time (<20 s) and the detection limit was as low as 0.11 μM. In addition, IrCN exhibited high selectivity towards ClO^- even in the presence of other competing species. Furthermore, IrCN was successfully integrated in fluorescent test strips for real-time detection of ClO^-.

Inorganic Complexes and Metal-Based Nanomaterials for Infectious Disease Diagnostics

Infectious diseases claim millions of lives each year. Robust and accurate diagnostics are essential tools for identifying those who are at risk and in need of treatment in low-resource settings. Inorganic complexes and metal-based nanomaterials continue to drive the development of diagnostic platforms and strategies that enable infectious disease detection in low-resource settings. In this review, we highlight works from the past 20 years in which inorganic chemistry and nanotechnology were implemented in each of the core components that make up a diagnostic test. First, we present how inorganic biomarkers and their properties are leveraged for infectious disease detection. In the following section, we detail metal-based technologies that have been employed for sample preparation and biomarker isolation from sample matrices. We then describe how inorganic- and nanomaterial-based probes have been utilized in point-of-care diagnostics for signal generation. The following section discusses instrumentation for signal readout in resource-limited settings. Next, we highlight the detection of nucleic acids at the point of care as an emerging application of inorganic chemistry. Lastly, we consider the challenges that remain for translation of the aforementioned diagnostic platforms to low-resource settings.

Arsenic Monitoring in Water by Colorimetry Using an Optimized Leucomalachite Green Method

Arsenic contamination of drinking water is a global concern. Standard laboratory methods that are commonly used for arsenic detection in water, such as atomic absorption spectroscopy and mass spectroscopy, are not suitable for mass monitoring purposes. Autonomous microfluidic detection systems combined with a suitable colorimetric reagent could provide an alternative to standard methods. Moreover, microfluidic detection systems would enable rapid and cost efficient in situ monitoring of water sources without the requirement of laborious sampling. The aim of this study is to optimize a colorimetric method based on leucomalachite green dye for integration into a microfluidic detection system. The colorimetric method is based on the reaction of arsenic (III) with potassium iodate in acid medium to liberate iodine, which oxidizes leucomalachite green to malachite green. A rapid colour development was observed after the addition of the dye. Beer's law was obeyed in the range between 0.07⁻3 µg mL-1. The detection limit and quantitation limit were found to be 0.19 and 0.64 µg mL-1, respectively.

A novel fluorometric method for inorganic pyrophosphatase detection based on G-quadruplex-thioflavin T

In this paper, we propose a fluorometric approach for the highly sensitive detection of inorganic pyrophosphatase (PPase) based on G-quadruplex-thioflavin T (ThT). In the absence of PPase, Cu²⁺ can coordinate with pyrophosphate (PPi) to generate a Cu²⁺/PPi complex. Then the G-rich sequence folds into the G-quadruplex structure, which can combine with ThT to generate a remarkable fluorescent signal. In the presence of PPase, the coordinated compound can be destroyed by the PPase catalyzed hydrolysis of PPi into inorganic phosphate (Pi). The subsequent release of Cu²⁺ can compete with ThT to induce a tighter G-quadruplex structure, causing the release of ThT and a sharp fluorescence decrease. Based on this mechanism, a facile and quantitative strategy for PPase detection was developed. The fluorescence intensity of the system shows a linear relationship with the PPase activities in the range of 0.5-30 U/L with a detection limit as low as 0.48 U/L. The proposed strategy for fluorescence spectrometric PPase detection is convenient, cost effective, and sensitive. This can be utilized to evaluate the inhibition effect of NaF on PPase as well as diagnose PPase-related diseases.

Label-free molecular probe based on G-quadruplex and strand displacement for sensitive and selective detection and naked eye discrimination of exon 2 deletion of AIMP2

Exon 2 deletion of aminoacyl tRNA synthetase complex-interacting multifunctional protein 2 (AIMP2) is a genetic deletion related to various cancers, for instance ovarian and lung cancers. It can be worked as an indicator of cancer for diagnosis of diseases. Here, we developed a label-free method based on the formation of split G-quadruplex in the presence of target DNA combined with strand displacement to detect exon 2 deletion of AIMP2 (DE2) sensitively and selectively. This method is easy-operating and cost-saving. Moreover, it has observed discrimination of gene deletion from wild-types by naked eyes. The results demonstrate that this strategy can be further used for the detection of different gene deletions to achieve early diagnosis of diseases and allow better prognosis.

Thiazole Orange-Modified Carbon Dots for Ratiometric Fluorescence Detection of G-Quadruplex and Double-Stranded DNA

A new carbon dot (CD)-based nanoprobe for the ratiometric fluorescence detection of DNA was constructed in this work. Thiazole orange (TO), a specific organic small molecular probe toward DNA, is covalently linked to the surface of CDs, acting as the recognition element and the fluorescence response unit. In the absence of DNA, the nanoprobe only emitted the blue fluorescence of CDs, whereas TO was almost nonfluorescent. Upon addition of DNA, a turn-on emission at 530 nm appeared and gradually enhanced along with the increasing of the target DNA, whereas the fluorescence of CDs was unchanged, which realized the ratiometric detection of the target DNA. The CD-TO nanoprobe showed good selectivity to parallel G-quadruplex (G4) and double-stranded (ds) DNA over antiparallel G4 and single-stranded DNA. Moreover, the ratiometric fluorescence nanoprobe exhibited high sensitivity for ssab (a dsDNA) and c-myc (a parallel G4) with a low detection limit of 0.90 and 3.31 nM, respectively. Additionally, the G4/hemin peroxidase activity inhibition experiment demonstrated that CD-TO bound to the G4s through the end-stacking mode.

Development of microfluidic platforms for the synthesis of metal complexes and evaluation of their DNA affinity using online FRET melting assays

Guanine-rich DNA sequences can fold into quadruple-stranded structures known as G-quadruplexes. These structures have been proposed to play important biological roles and have been identified as potential drug targets. As a result, there is increasing interest in developing small molecules that can bind to G-quadruplexes. So far, these efforts have been mostly limited to conventional batch synthesis. Furthermore, no quick on-line method to assess new G-quadruplex binders has been developed. Herein, we report on two new microfluidic platforms to: (a) readily prepare G-quadruplex binders (based on metal complexes) in flow, quantitatively and without the need for purification before testing; (b) a microfluidic platform (based on FRET melting assays of DNA) that enables the real-time and on-line assessment of G-quadruplex binders in continuous flow.

Recent progress and developments of iridium-based compounds as probes for environmental analytes

Metal complexes based on iridium metal centers have attracted attention as probes due to their tunable biological and chemical characteristics.

Glycodendron–rhenium complexes as luminescent probes for lectin sensing

Enhanced emission intensity of novel Re(i)-glycoprobes resulting from the specific recognition of carbohydrate-binding proteins as a potential tool in bioimaging applications.

Green synthesis of surface-passivated carbon dots from the prickly pear cactus as a fluorescent probe for the dual detection of arsenic(iii) and hypochlorite ions from drinking water

Efforts were made to develop a simple new approach for the green synthesis of surface-passivated carbon dots from edible prickly pear cactus fruit as the carbon source by a one-pot hydrothermal route. Glutathione (GSH) was passivated on the surface of the CDs to form a sensor probe, which exhibited excellent optical properties and water solubility. The prepared sensor was successfully characterized by UV-visible spectrophotometry, fluorescence spectrophotometry, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The simple sensing platform developed by the GSH-CDs was highly sensitive and selective with a “turn-off” fluorescence response for the dual detection of As³⁺ and ClO⁻ ions in drinking water. This sensing system exhibited effective quenching in the presence of As³⁺ and ClO⁻ ions to display the formation of metal complexes and surface interaction with an oxygen functional group. The oxygen-rich GSH-CDs afforded a better selectivity for As³⁺/ClO⁻ ions over other competitive ions. The fluorescence quenching measurement quantified the concentration range as 2–12 nM and 10–90 μM with the lower detection limit of 2.3 nM and 0.016 μM for the detection of As³⁺ and ClO⁻ ions, respectively. Further, we explored the potential applications of this simple, reliable, and cost-effective sensor for the detection of As³⁺/ClO⁻ ions in environmental samples for practical analysis.

Efforts were made to develop a simple new approach for the green synthesis of surface-passivated carbon dots from edible prickly pear cactus fruit as the carbon source by a one-pot hydrothermal route.

The Development of G-Quadruplex-Based Assays for the Detection of Small Molecules and Toxic Substances

G-Quadruplexes can be induced to form guanine-rich DNA sequences by certain small molecules or metal ions. In concert with an appropriate signal transducer, such as a fluorescent dye or a phosphorescent metal complex, the ligand-recognition event can be transduced into a luminescent response. This focus review aims to highlight recent examples of aptamer-based and metal-mediated G-quadruplex assays for the detection of small molecules and toxic substances in the last three years. We discuss the mechanisms and features of the different assays and present an outlook and a perspective for the future of this field.

Luminescent Strategies for Label-Free G-Quadruplex-Based Enzyme Activity Sensing

By catalyzing highly specific and tightly controlled chemical reactions, enzymes are essential to maintaining normal cellular physiology. However, aberrant enzymatic activity can be linked to the pathogenesis of various diseases. Therefore, the unusual activity of particular enzymes can represent testable biomarkers for the diagnosis or screening of certain diseases. In recent years, G-quadruplex-based platforms have attracted wide attention for the monitoring of enzymatic activities. In this Personal Account, we discuss our group's works on the development of G-quadruplex-based sensing system for enzyme activities by using mainly iridium(III) complexes as luminescent label-free probes. These studies showcase the versatility of the G-quadruplex for developing assays for a variety of different enzymes.

An electrochemiluminescence cloth-based biosensor with smartphone-based imaging for detection of lactate in saliva

An electrochemiluminescence cloth-based biosensor with smartphone-based imaging is firstly proposed, and is applied for facile detection of lactate in saliva.

A long-lived iridium(iii) chemosensor for the real-time detection of GHB

In this work, a long-lived iridium(iii) chemosensor 1 has been synthesized for the detection of GHB. The luminescence signal of iridium(iii) complex 1 could also be distinguished from strongly fluorescent media using time-resolved emission spectroscopy.