Signal switching electrochemical and fluorescence dual-mode sensing platform for carbendazim determination based on "two-in-one" magneto-fluorescent Cdots

An innovative method for carbendazim (CBZ) detection was developed, consisting of an electrochemical-fluorescence dual-mode biosensor based on magneto-fluorescent composite M-CDs. M-CDs, as the fluorescent probe of this sensor, could combine the electrical signal-ferrocene to achieve the "signal switching" by specifically recognizing CBZ through aptamers, of which magnetic property was used to quickly separate from complex substrates without interference. The dual-mode sensor based on M-CDs demonstrated excellent linear responses in both electrochemical and fluorescence assays. It achieved detection ranges of 10 fg/mL - 300 ng/mL and 60 fg/mL - 100 ng/mL with detection limits (LODs) of 1.4 fg/mL and 2.3 fg/mL. The sensor exhibited exceptional detection performance, stability and anti-interference. In addition, the results of the sensor in actual samples were consistent with those of enzyme-linked immunosorbent assay (ELISA), which further demonstrated that the sensor could accurately trace detecting CBZ in real samples and had a certain application prospect.

The Brown Sugar Mediated Carbon Quantum Dots as a Novel Fluorescence Sensor for Sensitive Detection of Gentamicin and Its Application in Foods

In this work, a novel fluorescence sensing strategy was proposed for the detection of gentamicin based on fluorescent carbon quantum dots (CQDs) and gold nanoparticles (AuNPs). Herein, the CQDs were green-synthesized for the first time via a one-step hydrothermal method utilizing brown sugar as the precursor. In the presence of citrate-stabilized AuNPs, the fluorescence of CQDs was quenched efficiently. Gentamicin, on the other hand, had a higher affinity for AuNPs and was able to compete with CQDs for a preferential binding to AuNPs, which ultimately led to the aggregation of AuNPs and freeing of CQDs in solution, causing the fluorescence recovery of CQDs. Based on the above phenomenon, the concentrations of gentamicin could be ascertained by detecting the variations in fluorescence intensity of CQDs. This sensing strategy exhibited excellent selectivity in various antibiotics. At the same time, the method displayed outstanding sensitivity for gentamicin, which was successfully applied to real samples detection.

Photophysical Study of Heteroatom-Doped Carbon Dots-MnO2-Based Nanosensor: Selective Detection of Glutathione in the Nanomolar Level

Heteroatom doping on carbon dots (Cdots) has been developed as an efficient approach to modify its optical and electronic properties. The four different types of heteroatom-doped Cdots (undoped Cdots (u-Cdots, nitrogen-doped Cdots (N-Cdots), sulfur-doped Cdots (Cdots), nitrogen, sulfur codoped Cdots (N, S-Cdots)) have been synthesized through a simple heat treatment of 5 min. Among four different heteroatoms doped nanosensors, N, S-Cdots with MnO2 nanospheres (Mn NS) showed one of the best fluorescents "on-off-on" nanosensors for selective sensing of glutathione (GSH) and cell imaging. N, S-Cdots showed a high fluorescence quantum yield, good photostability, ionic strength, and pH stability. N, S-Cdots with Mn NS demonstrated extremely high fluorescence quenching efficiency and the maximum fluorescence recovery rate after adding GSH to the produced solution. The photophysical study of N, S-Cdots-Mn NS used as a sensor confirms the inner filter effect (IFE) quenching mechanism between them. The developed sensor has an 80 nM limit of detection (LOD) for GSH. The heteroatom-doped framework of Cdots plays a significant role in the sensitive detection of GSH. N, S-Cdots-Mn NS have good permeability, biocompatibility, and low toxicity, due to which it was used in the intracellular imaging of GSH in living cells. The prepared sensor is rapid, economical, less toxic, and highly applicable in diagnosing diseases.

A facile approach for sulphur and nitrogen co-doped carbon nanodots to improve photothermal eradication of drug-resistant bacteria

In this study, we produced S, N co-doped CNDs (SN@CNDs) by using dimethyl sulfoxide (DMSO) and formamide (FA) as single sources of S and N, respectively. We varied the S/N ratios by adjusting the volume ratios of DMSO and FA and investigated their effect on the red-shift of the CNDs' absorption peak. Our findings demonstrate that SN@CNDs synthesized using a volume ratio of 5:6 between DMSO and FA exhibit the most significant absorption peak redshift and enhanced near-infrared absorption performance. Based on comparative analysis of the particle size, surface charge, and fluorescence spectrum of the S@CNDs, N@CNDs, and SN@CNDs, we propose a possible mechanism to explain the change of optical properties of CNDs due to S, N doping. Co-doping creates a more uniform and smaller band gap, resulting in a shift of the Fermi level and a change in energy dissipation from radioactive to non-radiative decay. Importantly, the as-prepared SN@CNDs exhibited a photothermal conversion efficiency of 51.36% at 808 nm and demonstrated exceptional photokilling effects against drug-resistant bacteria in both in vitro and in vivo experiments. Our facile method for synthesizing S and N co-doped CNDs can be extended to the preparation of other S and N co-doped nanomaterials, potentially improving their performance.

Review on Carbon Dot-Based Fluorescent Detection of Biothiols

Biothiols, such as cysteine (Cys), homocysteine (Hcy), and glutathione (GSH), play a vital role in gene expression, maintaining redox homeostasis, reducing damages caused by free radicals/toxins, etc. Likewise, abnormal levels of biothiols can lead to severe diseases, such as Alzheimer's disease (AD), neurotoxicity, hair depigmentation, liver/skin damage, etc. To quantify the biothiols in a biological system, numerous low-toxic probes, such as fluorescent quantum dots, emissive organic probes, composited nanomaterials, etc., have been reported with real-time applications. Among these fluorescent probes, carbon-dots (CDs) have become attractive for biothiols quantification because of advantages of easy synthesis, nano-size, crystalline properties, low-toxicity, and real-time applicability. A CDs-based biothiols assay can be achieved by fluorescent "Turn-On" and "Turn-Off" responses via direct binding, metal complex-mediated detection, composite enhanced interaction, reaction-based reports, and so forth. To date, the availability of a review focused on fluorescent CDs-based biothiols detection with information on recent trends, mechanistic aspects, linear ranges, LODs, and real applications is lacking, which allows us to deliver this comprehensive review. This review delivers valuable information on reported carbon-dots-based biothiols assays, the underlying mechanism, their applications, probe/CDs selection, sensory requirement, merits, limitations, and future scopes.

Use of metal nanoparticles for preconcentration and analysis of biological thiols

Metal nanoparticles (NPs) exhibit several unique physicochemical properties, including redox activity, surface plasmon resonance, ability to quench fluorescence, biocompatibility, or a high surface-to-volume ratio. They are being increasingly used in analysis and preconcentration of thiol containing compounds, because they are able to spontaneously form a stable Au/Ag/Cu-S dative bond. They thus find wide application in environmental and particularly in medical science, especially in the analysis of biological thiols, the endogenous compounds that play a significant role in many biological systems. In this review article, we provide an overview of various types of NPs that have been applied in analysis and preconcentration of biological thiols, mainly in human biological fluids. We first discuss shortly the types of NPs and their synthesis, properties, and their ability to interact with thiol compounds. Then we outline the sample preconcentration and analysis methods that were used for this purpose with special emphasis on optical, electrochemical, and separation techniques.

Selective and sensitive fluorescence turn-on detection of bilirubin using resorcinol-sucrose derived carbon dot

Carbon dots have been prepared from resorcinol and sucrose (rsCDs) hydrothermally, which show green emission at 525 nm with a fluorescence quantum yield (PLQY) of 17.2%. The intense emission of rsCDs is quenched upon the addition of Cu²⁺. In the presence of bilirubin (BR), the emission intensity is enhanced due to the competitive binding of Cu²⁺ with bilirubin and hence releasing rsCDs to the sensing medium. It is the first time report on turn-on fluorescence sensing towards BR with a detection limit of 85 nM. Even in the presence of other comparable biomolecules, the sensor is selective and ultrasensitive to bilirubin. A cellulose paper-based sensor strip has also been designed for the naked-eye detection of BR in blood serum. Due to the specific recognition of this rsCDs towards BR, it can be applied to detect BR in practical human serum samples.

Integration detection of mercury(ii) and GSH with a fluorescent "on-off-on" switch sensor based on nitrogen, sulfur co-doped carbon dots

Using aurine and citric acid as precursors, we have synthesized stable blue-fluorescent nitrogen and sulfur co-doped carbon dots (NS-CDs), with a high quantum yield of up to 68.94% via a thermal lysis method. The fluorescent NS-CDs were employed as a sensitive sensor for the integration detection of Hg2+ and glutathione (GSH). This was attributed to Hg2+ effectively quenching the fluorescence of the NS-CDs by static quenching, and then GSH was able to recover the fluorescence owing to the stronger binding between Hg2+ and the sulfhydryl of GSH. Based on the "on-off-on" tactic, the detection limits of Hg2+ ions and GSH were 50 nM and 67 nM respectively. The fluorescence sensor was successfully applied to detect Hg2+ ions and GSH in actual samples (tap water and fetal bovine serum). Furthermore, we have proved that the sensor had good reversibility. Overall, our NS-CDs can serve as effective sensors for environmental and biological analysis in the future.

A sensitive and rapid detection of glutathione based on a fluorescence-enhanced "turn-on" strategy

Glutathione (GSH) plays important roles in the human body including protecting cells from oxidative damages and maintaining cellular redox homeostasis. Thus, developing a fast and sensitive method for detecting GSH levels in living bodies is of great importance. Many methods have been developed and used for GSH detection, such as high-performance liquid chromatography, capillary electrophoresis, and fluorescence resonance energy-based methods. However, these methods often lack sensitivity as well as efficiency. Herein, a rapid and sensitive method for glutathione detection was developed based on a fluorescence-enhanced "turn-on" strategy. In this study, a unique and versatile bifunctional linker 3-[(2-aminoethyl) dithio]propionic acid (AEDP)-modified gold nanoparticle (Au@PLL-AEDP-FITC) probe was designed for the simple, highly sensitive intracellular GSH detection, combined with the FRET technique. In the presence of GSH, the disulfide bonds of AEDP on Au@PLL-AEDP-FITC were broken through competition with GSH, and FITC was separated from gold nanoparticles, making the fluorescence signal switch to the "turn on" state. A change in the fluorescence signal intensity has a great linear positive correlation with GSH concentration, in the linear range from 10 nM to 180 nM (R2 = 0.9948), and the limit of detection (LOD) of 3.07 nM, which was lower than other reported optical nanosensor-based methods. Au@PLL-AEDP-FITC also has great selectivity for GSH, making it promising for application in complex biological systems. The Au@PLL-AEDP-FITC probe was also successfully applied in intracellular GSH imaging in HeLa cells with confocal microscopy. In short, the Au@PLL-AEDP-FITC probe-based fluorescence-enhanced "turn-on" strategy is a sensitive, fast, and effective method for GSH detection as compared with other methods. It can be applied in complex biological systems such as cell systems, with promising biological-medical applications in the future.

Exploiting deep learning for predictable carbon dot design

In this study, we developed a deep convolution neural network (DCNN) model for predicting the optical properties of carbon dots (CDs), including spectral properties and fluorescence color under ultraviolet irradiation. These results demonstrate the powerful potential of DCNN for guiding the synthesis of CDs.

A peptide nucleic acid-regulated fluorescence resonance energy transfer DNA assay based on the use of carbon dots and gold nanoparticles

A convenient fluorometric method was developed for specific determination of DNA based on peptide nuclei acid (PNA)-regulated fluorescence resonance energy transfer (FRET) between carbon dots (CDs) and gold nanoparticles (AuNPs). In this system, CDs that display lake blue fluorescence with excitation/emission maxima at 345/445 nm were used as fluorometric reporter, while AuNPs were used as fluorescence nanoquencher. A neutral PNA probe, which is designed to recognize the target DNA, was used as a coagulant to control the dispersion and aggregation of AuNPs. Without DNA, PNA can induce immediate AuNP aggregation, thus leading to the recovery of the FRET-quenched fluorescence emission of CDs. However, the addition of the complementary target DNA can protect AuNPs from being aggregated due to the formation of DNA/PNA complexes, which subsequently produces a high fluorescence quenching efficiency of CDs by dispersed AuNPs. Under optimized conditions, quantitative evaluation of DNA was achieved in a linear range of 5-100 nM with a detection limit of 0.21 nM. This method exhibited an excellent specificity towards fully matched DNA. In addition, the application of this assay for sensitive determination of DNA in cell lysate demonstrates its potential for bioanalysis and biodetection. Graphical abstract A simple fluorometric biosensor for specific detection of DNA was developed based on peptide nuclei acid (PNA)-regulated fluorescence resonance energy transfer (FRET) between carbon dots (CDs) and gold nanoparticles (AuNPs).

A facile synthesis of magnetic fluorescence Fe3O4-carbon dots for the detection and removal of Hg2+

This article reports a one-pot hydrothermal strategy for preparing fluorescence carbon dots with magnetic properties (Fe₃O₄-CDs). The Fe₃O₄-CDs can be utilized for the detection of Hg²⁺, simultaneously accompanied with a magnetic removal process.

Sensitively and Selectively Detect Biothiols by Using Fluorescence Method and Resonance Light Scattering Technique Simultaneously

In this paper, we designed a new quantitative and qualitive detection method for biothiols by using fluorescence method and resonance light scattering (RLS) technique. Nitrogen doped carbon quantum dots (C/N-dots) were obtained from tartaric acid and ethylenediamine by hydrothermal method, and then their morphology and optical properties were characterized by different techniques. A detection system consisting of C/N-dots and Ag⁺ complex was established. In this system, C/N-dots possessed the photoluminescent property and the Ag⁺ complex owned the RLS property, so, by combining the two luminescent properties to achieve complementary advantages, we could detect biothiols and solve the problem of distinguishing between Cys and GSH. Additionally, we optimized detecting conditions and investigated the detection mechanism of fluorescence quenching and RLS detecting. Results showed that the analytical response of fluorescence was linear in the range 0–140 μM and the detection limit (LOD) was calculated to be 6.6 μM for Cys, and the addition of GSH had no effect on fluorescence. RLS response ranges were 0–167 μM for Cys and 0–200 μM for GSH, with LOD down to 64 nM and 74 nM, respectively. Furthermore, the probe was successfully used for detecting Cys in fetal bovine serum (FBS) samples by fluorescence method, and also, by RLS technique, the content of GSH in FBS samples was detected.

Modification of N,S co-doped graphene quantum dots with p-aminothiophenol-functionalized gold nanoparticles for molecular imprint-based voltammetric determination of the antiviral drug sofosbuvir

A molecularly imprinted polymer (MIP) was developed for the electrochemical determination of the antiviral drug sofosbuvir (SOF). The MIP was obtained by polymerization of p-aminothiophenol (p-ATP) on N,S co-doped graphene quantum dots (N,S@GQDs) in the presence of gold nanoparticles to form gold-sulfur covalent network. The presence of quantum dots improves the electron transfer rate, enhances surface activity and amplifies the signal. The nanocomposites were characterized by FTIR, TEM, EDX, and SEM. The electrochemical performance of the electrode was investigated by differential pulse voltammetry and cyclic voltammetry. The sensor uses hexacyanoferrate as the redox probe and is best operated at a potential of around 0.36 V vs. Ag/AgCl. It has a linear response over the concentration range of 1-400 nM SOF, with a detection limit of 0.36 nM. Other features include high selectivity, good reproducibility and temporal stability. The sensor was applied to the determination of SOF in spiked human plasma. Graphical abstract Novel sofosbuvir imprinted p-ATP polymer was synthesized by the aid of gold nanoparticles on N,S co-doped graphene quantum dots as a good conductive support. The imprinted polymer was used for detection of sofosbuvir in real samples by using the ferri/ferrocyanide redox probe.

One-Step Synthesis of Label-Free Ratiometric Fluorescence Carbon Dots for the Detection of Silver Ions and Glutathione and Cellular Imaging Applications

The construction of ratiometric fluorescence assay has displayed fantastic advantages in improving semi-quantitative visualization capability by presenting successive color changes. Herein, long-wavelength emission nitrogen-doped carbon dots (N-CDs) were developed for intrinsic ratiometric detection of silver ions (Ag⁺) and glutathione (GSH), accompanied by visualization fluorescence variation of orange and green. The label-free N-CDs were favorably obtained through one-step hydrothermal synthesis and displayed single long-wavelength emission at 618 nm under the excitation wavelength of 478 nm. Interestingly, a ratio rising peak emerges at 532 nm and the emission at 618 nm decreases with the introduction of Ag⁺, which exhibits ratiometric fluorescence emission characteristics ( I_618nm/ I_532nm) in the range of 0-140 μM with significant fluorescence varying from orange to green. Furthermore, the fluorescence of CDs@Ag(I) can be effectively ratiometric recovered by virtue of a specific reaction of GSH with Ag⁺, which is accompanied by the fluorescence of the solution returning from green to orange. In addition, the N-CDs hold excellent biocompatibility which can be implemented as the visualization biosensing platform for intracellular determination of Ag⁺ and GSH, demonstrating that proposed N-CDs have tremendous potential in biological systems.

pH-Dependent photoluminescence “switch-on” nanosensors composed of silver nanoparticles and nitrogen and sulphur co-doped carbon dots for discriminative detection of biothiols

A nanomaterial surface energy transfer (NSET) system composed of silver nanoparticles (AgNPs) and nitrogen and sulphur co-doped carbon dots (N,S-CDs) was established to discriminate biothiols, featuring the pH-promoted distinct PL “switch-on” response.

Reduced graphene oxide-supported methylene blue nanocomposite as a glucose oxidase-mimetic for electrochemical glucose sensing

A novel electrochemical glucose sensor based on methylene blue-reduced graphene oxide nanocomposite was constructed, and the sensor exhibited good glucose oxidase-mimetic electrocatalytic activity towards glucose and practical applicability.