Insight into the DNA adsorption on nitrogen-doped positive carbon dots

Emerging Trends of Carbon-Based Quantum Dots: Nanoarchitectonics and Applications

Carbon-based quantum dots (QDs) have emerged as a fascinating class of advanced materials with a unique combination of optoelectronic, biocompatible, and catalytic characteristics, apt for a plethora of applications ranging from electronic to photoelectrochemical devices. Recent research works have established carbon-based QDs for those frontline applications through improvements in materials design, processing, and device stability. This review broadly presents the recent progress in the synthesis of carbon-based QDs, including carbon QDs, graphene QDs, graphitic carbon nitride QDs and their heterostructures, as well as their salient applications. The synthesis methods of carbon-based QDs are first introduced, followed by an extensive discussion of the dependence of the device performance on the intrinsic properties and nanostructures of carbon-based QDs, aiming to present the general strategies for device designing with optimal performance. Furthermore, diverse applications of carbon-based QDs are presented, with an emphasis on the relationship between band alignment, charge transfer, and performance improvement. Among the applications discussed in this review, much focus is given to photo and electrocatalytic, energy storage and conversion, and bioapplications, which pose a grand challenge for rational materials and device designs. Finally, a summary is presented, and existing challenges and future directions are elaborated.

Enhanced Response Speed in 2D Perovskite Oxides-Based Photodetectors for UV Imaging through Surface/Interface Carrier-Transport Modulation

The long-time decay process induced by the persistent photoconductivity (PPC) in metal oxides-based photodetectors (PDs) impedes our demands for high-speed photodetectors. 2D perovskite oxides, emerging candidates for future high-performance PDs, also suffer from the PPC effect. Here, by integrating 2D perovskite Sr₂Nb₃O₁₀ (SNO) nanosheets and nitrogen-doped graphene quantum dots (NGQDs), a unique nanoscale heterojunction is designed to modulate surface/interface carrier transport for enhanced response speed. Notably, the decay time is reduced from hundreds of seconds to a few seconds. The 4%NGQDs-SNO PD exhibits excellent performance with a photocurrent of 0.47 μA, a high on-off ratio of 2.2 × 10⁴, and a fast pulse response speed (τ_decay = 67.3 ms), making it promising for UV imaging. The trap-involved decay process plays a dominant role in determining the decay time, resulting in the PPC effect in SNO PD, and the trap states mainly originate from oxygen vacancies and chemisorbed oxygen molecules. A significantly enhanced photoresponse speed in NGQDs-SNO PDs can be ascribed to the modulated surface/interface trap states and the efficient carrier pathway provided by the nanoscale heterojunction. This work provides an effective way to enhance the response speed in 2D perovskite oxides constrained by PPC via surface/interface engineering, promoting their applications in optoelectronics.

PDA-PEI-Copolymerized Nanodots with Tailorable Fluorescence Emission and Quenching Properties for the Sensitive Ratiometric Fluorescence Sensing of miRNA in Serum

Dopamine and polyethyleneimine (PEI) copolymerized nanodots (PDA-PEI nanodots) with both fluorescence emission and quenching features were synthesized by a simple one-step reaction at room temperature. By adjusting the dopamine and PEI ratio as well as the chain length of PEI, the fluorescence emission and quenching properties of PDA-PEI nanodots can be controlled well. Under optimal conditions, the nanodots showed strong green fluorescence emission with an absolute quantum yield of 1-2% and a quenching efficiency of more than 99% to several fluorophores with emission wavelengths ranging from blue to red light regions. The nanodots with a large number of functional groups also showed strong affinity to nucleic acid strands, excellent solubility in aqueous solution, long-term stability, and uniform size distribution. Integrating these attractive features with the specific enzymatic digestion reaction of the DSN enzyme, a highly sensitive ratiometric fluorescence nanoprobe for miRNA analysis was developed. Aminomethylcoumarin acetate (AMCA), which possesses the same excitation wavelength but a well-resolved blue fluorescence emission with PDA-PEI nanodots, was selected as the signal-reporting unit for capture probe labeling, while the inherent green fluorescence of PDA-PEI nanodots served as the reference. According to the ratiometric fluorescence signal, the ratiometric fluorescence nanoprobes showed high sensitivity and good accuracy for the miRNA assay. Because of the high and universal quenching efficiency, stable fluorescence emission, easily assembled interface, and uniform morphology, the nanodots may have great application prospects to serve as a universal nanoplatform for the fabrication of ratiometric fluorescence nanoprobes.

Leaching risks of antibiotic resistance genes in urban underlying surface sediments during the simulated stormwater runoff and its controls

Recently, increasing attention has been paid to antibiotic resistance genes (ARGs) in urban stormwater runoff. However, no available literature could be found on ARGs leaching from urban underlying surface sediments during stormwater runoff. In this study, surface sediments from commercial public squares around Nanjing (China) was selected for the investigation of target ARGs leaching kinetics, showing that absolute abundances of target ARGs desorption reached at the equilibrium during leaching time of 120-240min with all of the desorption efficiencies about 30%, indicating that there would be low proportion of leaching ARGs in the total ARGs migrating with runoff during rainfall events. Five target ARGs leaching including intI1 (clinic), strA, strB, tetM and tetX can be better described by the pseudo-second-order equation, while qacEdelta1 leaching can be better described by the pseudo-first-order equation, and the leaching for both sul1 and sul2 can be well described by the pseudo-first-order and pseudo-second-order equations. The effects of environmental factors including S/L ratios, pH values and water temperatures indicated that leaching efficiencies of target ARGs enhanced significantly with the increase of S/L ratios and water temperatures, but decreased with the increase of pH values. The transmission experiments after the simulated solar irradiation and heat implied that both large solar UV irradiation (30W/m²) and high temperature (40℃) were conducive to conjugation and transformation frequencies of ARGs. Furthermore, both high Cao and medium PAM levels could be effective for blocking ARGs transmission in the leachate from underlying surface sediments.

Nitrogen-Doped Carbon Dots for Selective and Rapid Gene Detection of Human Papillomavirus Causing Cervical Cancer

According to WHO, cervical cancer is considered as one of the most frequently diagnosed cancers and the fourth main source of cancer death in women in 2020 worldwide. Hence, there is a need for development of cervical cancer screening with new rapid and cost-effective methods. Although there are few methods available for HPV identification, these techniques are less sensitive, time-consuming, and costly. An ultra-sensitive, selective, and label-free DNA-based impedimetric electrochemical genosensor is developed in this study to detect HPV-18 for cervical cancer. Electrochemical analysis was performed for the characterization of the sensing platform and for the detection of analyte. A single-stranded 25mer oligonucleotide DNA probe was immobilized onto a nitrogen-doped carbon nanodot-modified ITO electrode. Furthermore, the hybridization event was measured by testing the complementary single stranded DNA sequence in the samples. The sensor could distinguish between complementary as well as non-complementary sequences. Herein, impedance quantification demonstrated a limit of detection of 0.405 fM. The developed genosensor showed high selectivity toward HPV-18 in the clinical samples. This sensing platform can be considered as a rapid and selective method for the screening of HPV-18.

Carbon Dots: An Innovative Tool for Drug Delivery in Brain Tumors

Brain tumors are particularly aggressive and represent a significant cause of morbidity and mortality in adults and children, affecting the global population and being responsible for 2.6% of all cancer deaths (as well as 30% of those in children and 20% in young adults). The blood-brain barrier (BBB) excludes almost 100% of the drugs targeting brain neoplasms, representing one of the most significant challenges to current brain cancer therapy. In the last decades, carbon dots have increasingly played the role of drug delivery systems with theranostic applications against cancer, thanks to their bright photoluminescence, solubility in bodily fluids, chemical stability, and biocompatibility. After a summary outlining brain tumors and the current drug delivery strategies devised in their therapeutic management, this review explores the most recent literature about the advances and open challenges in the employment of carbon dots as both diagnostic and therapeutic agents in the treatment of brain cancers, together with the strategies devised to allow them to cross the BBB effectively.

Antibacterial activity of positively charged carbon quantum dots without detectable resistance for wound healing with mixed bacteria infection

Widespread bacterial infection and the spread of antibiotic resistance exhibit increasing threat to the public and thus require new antibacterial strategies. Carbon quantum dots (CQDs) have been extensively investigated to play fluorescent, catalytic roles and even potential biomedical functions containing sterilization. However, synthetic understanding of the interaction of CQDs and bacteria, the exhibition of antibacterial ability, and the risk of resistance evolution remain lacking. Herein, a simple one-pot method was fabricated to prepare positively charged CQDs (PC-CQDs) as a broad-spectrum antibacterial agent. PC-CQDs possessed effective antibacterial activity against all tested Gram-positive, Gram-negative, and drug-resistant bacteria. Investigation of the antibacterial mechanism of PC-CQDs indicated that small-sized PC-CQDs functionalized with -NH₂ and -NH induced strong adherence behavior on the bacterial cell membrane. Moreover, the entry of PC-CQDs caused conformational changes in the genes and generation of reactive oxygen species in the bacteria. Safety evaluation illustrated that PC-CQDs did not trigger detectable drug resistance or hemolysis. Furthermore, PC-CQDs effectively promoted the antibacterial treatment of mixed Staphylococcus aureus and Escherichia coli infected wound in rats with low in vivo toxicity. These results suggested that PC-CQDs are a potential antibacterial candidate for real wound healing applications in complex bacterial infections and even resistant bacteria-caused infections.

Dual-probe fluorescent biosensor based on T7 exonuclease-assisted target recycling amplification for simultaneous sensitive detection of microRNA-21 and microRNA-155

Effective and simultaneous monitoring of the abnormal expression of certain microRNAs (miRNAs), especially for miRNA-21 and miRNA-155, can indicate drug resistance in lung cancer. In this work, T7 exonuclease (T7 Exo)-assisted target recycling amplification coupled with the extensive fluorescence quenching of graphene oxide (GO) was designed for the simultaneous detection of miRNA-21 and miRNA-155 using FAM- and ROX-labeled single-strand DNA probes. Through this method, the variable emission intensities of FAM and ROX caused by the introduction of miRNA-21 and miRNA-155, respectively, were obtained with high sensitivity. The method exhibited excellent analytical performance for simultaneous detection of miRNA-21 and miRNA-155 without cross-interference. The linear range was from 0.005 nM to 5 nM over three orders of magnitude, with detection limits as low as 3.2 pM and 4.5 pM for miRNA-21 and miRNA-155, respectively. Furthermore, the recovery (92.49-103.67%) and relative standard deviation (RSD < 4.8%) of the standard addition test of miRNA-21 and miRNA-155 in human plasma suggested the potential for drug resistance warning in clinical practice via this simple strategy. A homogeneous T7 Exo-assisted signal amplification combined with GO quenching platform was developed for accurate, sensitive and simultaneous analysis of miRNA-21 and miRNA-155 for drug resistance warning in lung cancer. This simple method exhibited a wide linear range and low LODs for miR-21 and miR-155.

Integration of fluorescent polydopamine nanoparticles on protamine for simple and sensitive trypsin assay

As an important protease, trypsin (TRY) has been identified as a key indicator of various diseases. A simple and sensitive strategy for TRY detection by using an environment-friendly biosafe probe is significant. Herein, we introduced negatively charged fluorescent polydopamine nanoparticles (PDNPs) with 4.8 nm diameter obtained through a controllable method as an effective probe for TRY. PDNPs exhibited excellent fluorescence property but integrated with protamine (Pro) to form an aggregation-caused quenching system via a static quenching mechanism. The quenching mechanism of Pro to PDNPs revealed the significant effect of the surface charge, functional groups, and appropriate size of PDNPs on quenching process. Given the specific hydrolysis of Pro by TRY, PDNPs were released from the quenching integration of PDNPs and Pro (PDNPs-Pro) and recovered their fluorescence. Thus, a fluorescence sensor for TRY with a linear range of 0.01 and 0.1 μg/mL and a detection limit of 6.7 ng/mL was developed without the disturbing from other proteases. Compared with other TRY assays, the biosensor based on PDNPs-Pro has the advantages of simple operation, environmental friendliness, and high sensitivity. This specific controlled-synthesis PDNPs would open up a new window for the extended application of fluorescent nanomaterials in biomedicine based on fluorescence changes induced by biological interaction.

Determination of chondroitin sulfate in synovial fluid and drug by ratiometric fluorescence strategy based on carbon dots quenched FAM-labeled ssDNA

Chondroitin sulfate (CS) plays an increasingly important role in clinical settings and pharmacy quality control. However, sensitive and simple methods for CS detection remain limited. In this work, positively charged nitrogen doped carbon dots (P-NCDs) with internal luminescence and quenching property to FAM-labeled random-sequence ssDNA (F-ssDNA) were prepared by a simple heating method. P-NCDs attached and quenched F-ssDNA through electrostatic interaction to form the system of P-NCDs and F-ssDNA (P-NCDs/F-ssDNA) with retained fluorescence intensity of P-NCDs. The highly negatively charged CS reacted electrostatically with P-NCDs and then replaced F-ssDNA in P-NCDs/F-ssDNA to recover the fluorescence intensity of the original quenched F-ssDNA while retaining the internal fluorescence intensity of P-NCDs. Thus, by using restored F-ssDNA as the signal controlled by adding CS to P-NCDs/F-ssDNA, a ratiometric fluorescence strategy based on the retained fluorescence of P-NCDs as reference signal was fabricated through synchronous fluorescence spectrometry for the sensitive detection of CS. Under the optimal experimental conditions, a linear equation for CS was obtained for CS concentration within the range of 0.05-2.0 μg/mL. The method was also successfully applied for the accurate determination of CS in joint fluid samples of arthritic patients, chondroitin sulfate tablets, and chondroitin sulfate eye drops, suggesting its appreciable application potential in the clinic.

A simple fluorescence assay for trypsin through a protamine-induced carbon quantum dot-quenching aggregation platform

The development of a simple detection strategy for trypsin (Try) is urgent, and is ascribed to the diagnostic value of Try in several diseases. Herein, a facile but effective fluorescence strategy for Try was developed based on the protamine (Pro)-induced aggregation of carbon quantum dots (CQDs). The fluorescence of negatively charged CQDs was quenched with Pro due to the assembly of CQDs and Pro (CQDs/Pro) through electrostatic interaction. However, the highly positively charged Pro, which is rich in basic arginine residues, was preferred to be hydrolyzed by Try. Try can induce the deaggregation of CQDs/Pro, thereby enabling the release of CQDs to restore the fluorescence intensity. Thus, the use of CQDs/Pro as a testing platform will be employed as a “turn-on” method for Try. In addition, the fluorescence-resuming response was proportional to Try, ranging from 25 ng mL⁻¹ to 500 ng mL⁻¹ with a limit of detection (LOD) of 8.08 ng mL⁻¹. This “turn-on” fluorescence assay for Try was label-free, convenient, and relatively free of interference from coexisting substances. Actual applications for Try monitoring and trypsin inhibitor screening also illustrated the considerable prospect of CQDs in the clinical field, combined with the superiority of the simple mixing operation.

In this work, a simple melting method was developed for carbon quantum dot fabrication to integrate with protamine as an effective signal-on fluorescence strategy for trypsin detection.

Fluorescence sensing of tyrosinase activity based on amine rich carbon dots through direct interaction in a homogeneous system: detection mechanism and application

As a vital, copper-containing oxidase, tyrosinase (TYR) is useful as a biomarker for the screening of skin diseases. In this paper, a convenient and sensitive homogeneous fluorescence detection platform for the assay of TYR activity without any modified steps is described. Inspired by the fact that carbon dots (CDs) with excellent properties can be obtained through some surface modification, amine rich carbon dots (N-CDs) using a nitrogen doping process were developed as the fluorescent probe for this assay. The effect and the response mechanism of the degree of nitrogen doping in relation to the response of different CDs to the sensing of TYR activity using dopamine (DA) as a substrate were investigated. The DA was oxidized to o-dopaquinone with the catalyzation of TYR and quenched the fluorescence of the N-CDs by direct interaction. By using a set concentration of DA and other optimized reaction conditions, the fluorescence intensity of the N-CDs was directly applied to monitor the TYR activity. This assay for TYR activity showed a broad linear range from 0.05 to 6.0 U mL-1 with a detection limit of 0.039 U mL-1. The satisfactory recovery of the sensor for TYR activity in diluted human serum illustrated a potential clinical application.