Sensitive and selective sensing system of metallothioneins based on carbon quantum dots and gold nanoparticles

Metal ion-complexed DNA probe coupled with CRISPR/Cas12a amplification and AuNPs for sensitive colorimetric assay of metallothionein in fish

The accurate and sensitive detection of metallothionein (MT) is of great significance in the fields of biomedical, toxicological and environmental sciences. In this work, based on the high affinity interaction between MT and the heavy metal ions of Hg2+ and the significant signal amplification capability of Cas12a/crRNA enzyme as well, we report a simple and highly sensitive method for visual detection of MT, a biomarker in fish for heavy metal ion-induced water bio-pollution. The target MT molecules bind Hg2+ in the Hg2+- complexed hairpin DNA probes to unfold the hairpin structure into ssDNAs, which hybridize with the partial dsDNA duplexes via strand displacement to yield specific sequence-containing dsDNAs. Cas12a/crRNA recognizes these specific sequences to activate its enzyme activity to cyclically cleave the ssDNA linkers in the blue colored gold nanoparticle aggregates to transit their color into red to realize visual detection of MT. Owing to the signal amplification by Cas12a/crRNA, as low as 25 nM of MT can be visually detected with naked eye. In addition, our colorimetric detection method has high selectivity for MT against other interference proteins and can detect MT in the livers and kidneys of crucian carps bought from a local supermarket. Moreover, the developed assay overcomes the limitations of conventional MT detection methods in terms of complexity, high cost and low sensitivity and can therefore offer new methods for monitoring water bio-pollutions.

Target-promoted autocatalytic hairpin assembly of bivalent DNAzymes for sensitive and label-free electrochemical metallothionein assay

Metallothionein (MT) has shown to be an important biomarker for environmental monitoring and various diseases, due to its significant binding ability to heavy metal ions. On the basis of such a characteristic and the Hg2+-stabilized DNA duplex (Hg2+-dsDNA) probe, as well as a new autocatalytic hairpin assembly (aCHA)/DNAzyme cascaded signal enhancement strategy, the construction of a highly sensitive and label-free electrochemical MT biosensor is described. Target MT molecules bind Hg2+ in Hg2+-dsDNA to disrupt the duplex structure and to release ssDNA sequences, which trigger subsequent aCHA for efficient production of mimic aCHA triggering strands and many bivalent DNAzymes. The signal hairpins on the electrode are then cyclically cleaved by DNAzyme amplification cascade to liberate plenty G-quadruplex sequences, which bind hemin and yield largely enhanced currents for sensitive assay of MT with a detection limit of 0.217 nM in a label-free approach. Such sensor also shows selective discrimination capability to MT against other interfering proteins and assay of MT in normal serums with dilution has also been verified, indicating its potential for highly sensitive detection of different heavy metal ion binding molecules for various application scenarios.

Ag+-stabilized DNA triplex coupled with catalytic hairpin assembly and CRISPR/Cas12a amplifications for sensitive metallothionein assay

Metallothionein (MT) is a protein biomarker secreted by liver in response to the treatment for heavy metal toxicity and oncological diseases. On the basis of a new Ag+-stabilized DNA triplex probe (Ag+-SDTP), we establish a fluorescent biosensing system for high sensitivity detection of MT by combining catalytic hairpin assembly (CHA) and the CRISPR/Cas12a signal enhancements. The MT analyte complexes with Ag+ in Ag+-SDTP to disrupt the triplex structure and to release the ssDNA strands, which trigger subsequent CHA formation of many protospacer adjacent motif (PAM)-containing dsDNAs from two hairpins. Cas12a/crRNA further recognizes these PAM sequences to activate its trans-catalytic activity to cyclically cleave the fluorescently quenched ssDNA reporters to recovery drastically amplified fluorescence for detecting MT down to 0.34 nM within the dynamic range of 1∼800 nM. Moreover, the sensing method is able to selectively discriminate MT from other non-specific molecules and can realize low level detection of MT in diluted human serums, manifesting its potentiality for monitoring the disease-specific MT biomarker at trace levels.

A highly sensitive fluorescence nanosensor for determination of amikacin antibiotics using composites of carbon quantum dots and gold nanoparticles

Amikacin is an aminoglycoside antibiotic widely used to treat various bacterial infections in humans. However, elevated concentrations of amikacin can damage the cochlear nerve. Thus, accurate and rapid amikacin detection is crucial. In this study, we developed an "on-off" fluorescence nanosensor for highly sensitive amikacin determination based on a composite of carbon quantum dots (CQDs) and gold nanoparticles (AuNPs). The method quenches CQD fluorescence (turn-off) when they bind to AuNPs but restores it (turn-on) when amikacin binds and releases the CQDs. Adding Cu2+ enhances sensitivity by cross-linking amikacin-coated AuNPs. Under optimal conditions (pH 4, 1 mM Na2SO4, 1 mM CuSO4), the method achieved a low detection limit of 3.5 × 10-11 M (0.02 ppb), a wide linear range (10-10 to 10-8 M), high precision (RSD < 5 %), and a rapid 2-minute response time. Exceptional selectivity was observed over other antibiotics. The CQDs/AuNPs-based sensor successfully detected amikacin in pharmaceutical and surface water samples. This approach offers a fast on-site analytical method for amikacin detection, with potential applications in clinical and environmental settings.

A metal ion-coordinated DNA probe for sensitive fluorescence detection of metallothionein via a dual nucleic acid amplification strategy

Sensitively monitoring metallothionein (MT), a heavy metal-binding protein with substantial cysteine content, is of significance for evaluating heavy metal poisoning in both humans and animals. Based on a new metal ion-coordinated DNA probe and the heavy metal ion binding capability of MT, as well as the substantial signal enhancement of the hybridization chain reaction (HCR) and rolling circle amplification (RCA), we demonstrate a highly sensitive fluorescence MT detection assay. MT binds the metal ions in the hairpin structured, metal ion-coordinated DNA probe to switch its hairpin structure into ssDNA, which triggers subsequent RCA reactions and HCRs to open plenty of fluorescently quenched signal hairpins to exhibit drastically amplified fluorescence recovery for assaying MT down to 0.58 nM within a dynamic range of 1-320 nM. In addition, the investigation of low contents of MT in diluted human serum by such an assay has also been verified, indicating its promising application potential for diagnosing heavy metal poisoning.

Characterization of the internal working-life exposome using minimally and non-invasive sampling methods - a narrative review

During recent years, we are moving away from the 'one exposure, one disease'-approach in occupational settings and towards a more comprehensive approach, taking into account the totality of exposures during a life course by using an exposome approach. Taking an exposome approach however is accompanied by many challenges, one of which, for example, relates to the collection of biological samples. Methods used for sample collection in occupational exposome studies should ideally be minimally invasive, while at the same time sensitive, and enable meaningful repeated sampling in a large population and over a longer time period. This might be hampered in specific situations e.g., people working in remote areas, during pandemics or with flexible work hours. In these situations, using self-sampling techniques might offer a solution. Therefore, our aim was to identify existing self-sampling techniques and to evaluate the applicability of these techniques in an occupational exposome context by conducting a literature review. We here present an overview of current self-sampling methodologies used to characterize the internal exposome. In addition, the use of different biological matrices was evaluated and subdivided based on their level of invasiveness and applicability in an occupational exposome context. In conclusion, this review and the overview of self-sampling techniques presented herein can serve as a guide in the design of future (occupational) exposome studies while circumventing sample collection challenges associated with exposome studies.

A sensitive fluorescence nanoplatform for monitoring benzoyl peroxide in food using carbon dots coupled with glutathione capped gold nanoparticles as FRET probe

Herein, a sensitive fluorescence nanoplatform for benzoyl peroxide (BPO) detection is constructed from carbon dots (CDs) and glutathione capped gold nanoparticles (GSH-AuNPs). The fluorescence of CDs is first quenched due to the fluorescence resonance energy transfer (FRET) effect in the presence of GSH-AuNPs, and then effectively recovered when adding BPO. The detection mechanism lies in the aggregation of AuNPs in a high salt background due to oxidation of GSH caused by BPO, thus the amount of BPO is reflected by the variations of the recovered signals. The linear range and detection limit in this detection system is found to be 0.05-200 μM (R² = 0.994) and 0.1 µg g^-1 (3σ/K), respectively. Several possible interferents with high concentration show little influence on BPO detection. The proposed assay exhibits good performance for BPO determination in wheat flour and noodles, demonstrating its applicability for facile monitoring BPO additive amount in real foods.

A smartphone-assisted ultrasensitive detection of acrylamide in thermally processed snacks using CQD@Au NP integrated FRET sensor

Selective, sensitive, and accurate detection of acrylamide (AA) in thermally processed food is a great challenge for food safety. This paper describes a "turn-on" fluorescence strategy to detect AA in real samples. Herein, the fluorescence intensity of glutathione-modified carbon quantum dots (GSHCQDs) was quenched initially upon the addition of gold nanoparticles (Au NPs) via fluorescence resonance electron transfer (FRET) to form a quenched GSHCQD-Au nanoprobe. When AA was introduced to the quenched GSHCQD-Au nanoprobe, the strong thiol-ene Michael addition (M-A) reaction among the -SH group of GSHCQD and AA occurred which releases GSHCQD to the medium and FL intensity at 520 nm is regained. The GSHCQD-Au nanoprobe can detect the AA in a normal aqueous solution (pH 7) selectively over a short response time of 5 min. Under the optimized conditions, the detection limit of AA was obtained to be 0.12 pM, over a wide linear range of 0-200 nM. Especially, this FRET-based sensing method was utilized successfully for the sensitive detection of AA using an RGB app installed on a smartphone, opening a new approach for the smart sensing of food contaminants.

Construction of mitochondria targeted and FRET based ratiometric sensing nanoplatform for sulfur dioxide accurate detection in vitro and in vivo

Sulfur dioxide (SO₂) is a key molecule in organisms that is involved in the regulation of different physiological procedures. Aberrant SO₂ causes a variety of diseases, such as cancer and neurodegeneration. Thus, sensitive and selective detection of SO₂ is of great importance. Based on the Förster resonance energy transfer (FRET) between green fluorescence carbon dots (GCDs) donor and amide-linked near-infrared fluorescence emissive organic small molecular dye (CDDBT) acceptor, one ratiometric fluorescent nano platform, Mito-GCDs-CDDBT for mitochondria SO₂ sensing was constructed. In this FRET sensing system, CDDBT served as the receptor for SO₂, and the presence of SO₂ enhanced GCDs green fluorescence signal and quenched CDDBT near-infrared fluorescence signal due to the disruption of FRET. Mito-GCDs-CDDBT could sensitively detect SO₂ with a detection limit of as low as 0.701 μM. Meanwhile, Mito-GCDs-CDDBT achieved fluorescence imaging to measure the response of cellular exogenous and endogenous SO₂ with remarkable mitochondrial targeting. Moreover, Mito-GCDs-CDDBT also realized SO₂ sensing in vivo including zebrafish and mice. The as-prepared versatile nanoplatform displayed several advantages, such as mitochondria targeting, FRET-based sensitive detection, and sensing capabilities in biological milieu. Potentially, it could be applied in the diagnostics of SO₂ involved diseases.

A fluorescent probe based on FRET effect between carbon nanodots and gold nanoparticles for sensitive detection of thiourea

Illegal abuse results in the presence of thiourea (TU) in soil, wastewater, and even fruits, which is harmful for the environment and human health. It has urgent practical significance to design an efficient and reliable probe for TU detection. Herein, a sensitive fluorescent probe with off-on response for harmful TU was reported. The probe was designed with fluorescent carbon nanodots (CNDs) and gold nanoparticles (AuNPs) based on fluorescence resonance energy transfer (FRET) effect. Firstly, the CNDs were pre-combined with AuNPs and the fluorescence of CNDs was quenched due to the FRET effect. Upon addition of TU, the fluorescence of CNDs recovered due to the unbinding of CNDs and AuNPs, since the coordination interaction between TU and AuNPs is stronger than the electrostatic interaction among CNDs and AuNPs. Under the optimum parameters, a linear relationship was found between the relative fluorescence intensity of the probe and the concentration of TU in the range of 5.00 × 10^-8-1.00 × 10^-6 M (R² = 0.9958), with the limit of detection (LOD) calculated to be 3.62 × 10^-8 M. This proposed method is easy to operate and has excellent selectivity and sensitivity for TU, which can be effectively applied in environmental water and compound fruit-vegetable juice.

Carbon Dots Conjugated Antibody as an Effective FRET-Based Biosensor for Progesterone Hormone Screening

In this work, carbon dots (CDs) were synthesized by a one-step hydrothermal method using citric acid and ethylene diamine, and covalently functionalized with antibodies for the sensing of progesterone hormone. The structural and morphological analysis reveals that the synthesized CDs are of average size (diameter 8-10 nm) and the surface functionalities are confirmed by XPS, XRD and FT-IR. Further graphene oxide (GO) is used as a quencher due to the fluorescence resonance energy transfer (FRET) mechanism, whereas the presence of the analyte progesterone turns on the fluorescence because of displacement of GO from the surface of CDs effectively inhibiting FRET efficiency due to the increased distance between donor and acceptor moieties. The linear curve is obtained with different progesterone concentrations with 13.8 nM detection limits (R2 = 0.974). The proposed optical method demonstrated high selectivity performance in the presence of structurally resembling interfering compounds. The PL intensity increased linearly with the increased progesterone concentration range (10-900 nM) under the optimal experimental parameters. The developed level-free immunosensor has emerged as a potential platform for simplified progesterone analysis due to the high selectivity performance and good recovery in different samples of spiked water.

Mechanisms for carbon dots-based chemosensing, biosensing, and bioimaging: A review

Due to the favorable biocompatibility, photostability and fluorescence emissions, carbon dots (CDs) are being widely investigated as fluorescent probes. Current CD-based fluorescent probe designs depend largely on conventional fluorescence sensing mechanisms, for e.g. the inner filter effect, photoinduced electron transfer, and Förster resonance energy transfer. Although these mechanisms have been successful, it is still desirable to introduce new sensing mechanisms. In recent years, emerging mechanisms such as aggregation-induced emission, hydrogen-bond induced emission, and intramolecular charge transfer have been developed for CD-based probes. This review summarizes both conventional and emerging mechanisms, and discuss CDs in the context of chemosensing, biosensing, and bioimaging. We provide an outlook for several other mechanisms such as CN isomerization, the short-wavelength inner filter technique, excited-state intramolecular proton transfer, and twisted intramolecular charge transfer, which have been applied to organic fluorescent probes design but not as much in CD-based sensing systems. We envision that this review will provide insights that inspire further development of CD-based fluorescent probes as for biological applications.

Selective and Sensitive Fluorometric Determination of Piroxicam Based on Nitrogen-doped Graphene Quantum Dots and Gold Nanoparticles Coated with Phenylalanine

In this study, a sensitive fluorimetric method is proposed for the determination of piroxicam using nitrogen graphene quantum dots (N-GQDs) and gold nanoparticles coated with phenylalanine. The fluorescence emission of N-GQDs at 440 nm decreases with the increase of gold nanoparticles coated with phenylalanine. However, the addition of piroxicam causes the release of gold nanoparticles from the surface of quantum dots followed by the retrieval of the fluorescence emission of N-GQDs. Under the optimum conditions, the calibration graph was linear in the concentration range of 2.0-35.0 nmol L^-1 for piroxicam with a limit of detection of 0.11 nmol L^-1. The developed method was successfully applied for the determination of piroxicam in urine and serum samples.

Recent advances in synthesis and modification of carbon dots for optical sensing of pesticides

Serious threat from pesticide residues to the ecosystem and human health has become a global concern. Developing reliable methods for monitoring pesticides is a world-wide research hotspot. Carbon dots (CDs) with excellent photostability, low toxicity, and good biocompatibility have been regarded as the potential substitutes in fabricating various optical sensors for pesticide detection. Based on the relevant high-quality publications, this paper first summarizes the current state-of-the-art of the synthetic and modification approaches of CDs. Then, a comprehensive overview is given on the recent advances of CDs-based optical sensors for pesticides over the past five years, with a particular focus on photoluminescent, electrochemiluminescent and colorimetric sensors regarding the sensing mechanisms and design principles by integrating with various recognition elements including antibodies, aptamers, enzymes, molecularly imprinted polymers, and some nanoparticles. Novel functions and extended applications of CDs as signal indicators, catalyst, co-reactants, and electrode surface modifiers, in constructing optical sensors are specially highlighted. Beyond an assessment of the performances of the real-world application of these proposed optical sensors, the existing inadequacies and current challenges, as well as future perspectives for pesticide monitoring are discussed in detail. It is hoped to provide powerful insights for the development of novel CDs-based sensing strategies with their wide application in different fields for pesticide supervision.

Carbon Nanomaterial-Based Drug Sensing Platforms Using State-of-the- Art Electroanalytical Techniques

Background:

Currently, nanotechnology and nanomaterials are considered as the most popular and outstanding research subjects in scientific fields ranging from environmental studies to drug analysis. Carbon nanomaterials such as carbon nanotubes, graphene, carbon nanofibers etc. and non-carbon nanomaterials such as quantum dots, metal nanoparticles, nanorods etc. are widely used in electrochemical drug analysis for sensor development. Main aim of drug analysis with sensors is developing fast, easy to use and sensitive methods. Electroanalytical techniques such as voltammetry, potentiometry, amperometry etc. which measure electrical parameters such as current or potential in an electrochemical cell are considered economical, highly sensitive and versatile techniques.

Methods:

Most recent researches and studies about electrochemical analysis of drugs with carbon-based nanomaterials were analyzed. Books and review articles about this topic were reviewed.

Results:

The most significant carbon-based nanomaterials and electroanalytical techniques were explained in detail. In addition to this; recent applications of electrochemical techniques with carbon nanomaterials in drug analysis was expressed comprehensively. Recent researches about electrochemical applications of carbon-based nanomaterials in drug sensing were given in a table.

Conclusion:

Nanotechnology provides opportunities to create functional materials, devices and systems using nanomaterials with advantageous features such as high surface area, improved electrode kinetics and higher catalytic activity. Electrochemistry is widely used in drug analysis for pharmaceutical and medical purposes. Carbon nanomaterials based electrochemical sensors are one of the most preferred methods for drug analysis with high sensitivity, low cost and rapid detection.

A MnO2 nanosheet-assisted ratiometric fluorescence probe based on carbon quantum dots and o-phenylenediamine for determination of 6-mercaptopurine

A MnO₂ nanosheet-assisted ratiometric fluorescence probe based on carbon quantum dots (CQDs) and o-phenylenediamine (OPD) has been developed for the detection of the anticancer drug 6-mercaptopurine (6-MP). CQDs with strong fluorescence are synthesized via the one-step hydrothermal method. MnO₂ nanosheets as an oxidase-mimicking nanomaterial directly oxidize OPD into 2,3-diaminophenazine (DAP) which has a fluorescence emission at 570 nm, whereas the fluorescence of CQDs at 445 nm is then reduced by the DAP through the inner filter effect (IFE) under a single excitation wavelength (370 nm). After adding 6-MP, MnO₂ nanosheets can be reduced to Mn²⁺ and lose their oxidase-like property, blocking the IFE with the fluorescence decrease of DAP and fluorescence increase of CQDs. The novel ratiometric fluorescence probe exhibits considerable sensitivity toward 6-MP and linear response is in the 0.46-100.0 μmol L^-1 concentration range with the detection limit of 0.14 μmol L^-1. Furthermore, the probe shows good selectivity when exposed to a series of interfering other organic and inorganic compounds, and biomolecules and can be applied to the detection for 6-MP in human serum samples and pharmaceutical tablets. Satisfactory recoveries of 6-MP in human serum samples are in the range 96.1-110.9% with the RSD of 1.4 to 3.2%. The amount of 6-MP is successfully estimated as 49.3 mg in pharmaceutical tablet with the RSD of about  2.2%.

Recent advances in the construction and analytical applications of carbon dots-based optical nanoassembly

Recently, more and more attention has been focused on the construction and analytical applications of optical nanoassembly through combining carbon dots (CDs) with various other functional nanomaterials. The rational design and manufacture of CDs-based optical nanoassembly will be critical to meeting the needs of analytical science. The last decade has witnessed the immense potential of CDs-based optical nanoassembly in multiple sensing applications owing to their controlled optical properties, adjustable surface chemistry and microscopic morphology. This feature article collects the recent advances in the research and development of CDs-based optical nanoassembly and their applications in analytical sensors, aiming to provide vital insights and suggestions to inspire their broad sensing applications.