Enzyme-free fluorescence determination of uric acid and trace Hg(II) in serum using Si/N doped carbon dots

Investigation of silicon doped carbon dots/Carboxymethyl cellulose gel platform with tunable afterglow and dynamic multistage anticounterfeiting

The remarkable optical properties of carbon dots, particularly their tunable room-temperature phosphorescence, have garnered significant interest. However, challenges such as aggregation propensity and complex phosphorescence control via energy level manipulation during synthesis persist. Addressing these issues, we present a facile gel platform for tunable afterglow materials. This involves chemically cross-linking biomass-derived silicon-doped carbon dots with carboxymethylcellulose and incorporating non-precious metal salts (BaCl2, CaCl2, MgCl2, ZnCl2, ZnBr2, ZnSO4) to enhance phosphorescence. Metal salts boost intersystem crossing via spin-orbit coupling, elevating triplet state transitions and activating phosphorescence. Chemical bonding and salt-induced coordination/electrostatic interactions establish confinement effects, suppressing non-radiative transitions. Diverse salt-gel interactions yield gels with tunable phosphorescence lifetimes (9.48 ms to 32.13-492.39 ms), corresponding to afterglow durations ranging from 3.20 to 11.86 s. With its broad tunability and high recognition, this gel material exhibits promising potential for dynamic multilevel anti-counterfeiting applications.

Silicon-Doped Carbon Dots Crosslinked Carboxymethyl Cellulose Gel: Detection and Adsorption of Fe3

The excessive emission of iron will pollute the environment and harm human health, so the fluorescence detection and adsorption of Fe3+ are of great significance. In the field of water treatment, cellulose-based gels have attracted wide attention due to their excellent properties and environmental friendliness. If carbon dots are used as a crosslinking agent to form a gel with cellulose, it can not only improve mechanical properties but also show good biocompatibility, reactivity, and fluorescence properties. In this study, silicon-doped carbon dots/carboxymethyl cellulose gel (DCG) was successfully prepared by chemically crosslinking biomass-derived silicon-doped carbon dots with carboxymethyl cellulose. The abundant crosslinking points endow the gel with excellent mechanical properties, with a compressive strength reaching 294 kPa. In the experiment on adsorbing Fe3+, the theoretical adsorption capacity reached 125.30 mg/g. The introduction of silicon-doped carbon dots confers the gel with excellent fluorescence properties and a good selective response to Fe3+. It exhibits a good linear relationship within the concentration range of 0-100 mg/L, with a detection limit of 0.6595 mg/L. DCG appears to be a good application prospect in the adsorption and detection of Fe3+.

A luminescent MOF-based nonenzymatic probe for colorimetric/photothermal/fluorescence triple-mode assay of uric acid in body fluids

Monitoring the levels of uric acid (UA) in body fluids is of great significance in the clinical diagnosis and therapy of related diseases. Herein, a novel nanocomposite R6G@Fe-MOF based nonenzymatic probe is presented to provide a ratiometric fluorescent, colorimetric, and photothermal triple read-out signal for the visual, sensitive, and convenient assay of UA. The framework structure of the in situ encapsulated R6G@Fe-MOF is found to decompose upon the addition of UA, resulting in the reduction of Fe3+ to Fe2+. This reduction will lead to a rapid increase in fluorescence emission (FL) at 430 nm. Simultaneously, the FL at 573 nm will decrease remarkably due to the inner filter effect (IFE) between UA and R6G@Fe-MOF. Furthermore, the reaction of the generated Fe2+ with potassium ferricyanide (K3 [Fe(CN)6]) can in situ generate Prussian blue (PBNPs) with outstanding color and photothermal properties, which allow for easy colorimetric and photothermal signal readout. The detection limits (LOD) for the colorimetric, fluorometric and photothermal detection are low at 1.68 μM, 0.236 μM, and 1.32 μM respectively. Ultimately, it is successfully employed to determine UA in urine, serum, and saliva, yielding satisfactory results. The constructed R6G@Fe-MOF sensor provides a simple, sensitive, and accurate determination of UA that can be tailored to meet the needs of various applications, and also provides new perspectives for the design and development of versatile sensors for diverse uses.

Organosilicon-Based Carbon Dots and Their Versatile Applications

Carbon dots (CDs) are a newly discovered type of fluorescent material that has gained significant attention due to their exceptional optical properties, biocompatibility, and other remarkable characteristics. However, single CDs have some drawbacks such as self-quenching, low quantum yield (QY), and poor stability. To address these issues, researchers have turned to organosilicon, which is known for its green, economical, and abundant properties. Organosilicon is widely used in various fields including optics, electronics, and biology. By utilizing organosilicon as a synthetic precursor, the biocompatibility, QY, and resistance to self-quenching of CDs can be improved. Meanwhile, the combination of organosilicon with CDs enables the functionalization of CDs, which significantly expands their original application scenarios. This paper comprehensively analyzes organosilicon in two main categories: precursors for CD synthesis and matrix materials for compounding with CDs. The role of organosilicon in these categories is thoroughly reviewed. In addition, the paper presents various applications of organosilicon compounded CDs, including detection and sensing, anti-counterfeiting, optoelectronic applications, and biological applications. Finally, the paper briefly discusses current development challenges and future directions in the field.

Two-dimensional glass/p-ATP/Ag NPs as multifunctional SERS substrates for label-free quantification of uric acid in sweat

Abnormal uric acid (UA) content in body fluids can fully reflect the status of metabolism and immunity in the body. We have developed a simple, efficient and label-free surface enhanced Raman scattering (SERS) method for UA detection. Briefly, p-aminothiophenol (p-ATP) was used as the internal standard molecule and linking molecule to prepare a glass/p-ATP/Ag NPs SERS substrate. The Raman characteristic peak of p-ATP at 1076 cm^-1 can be used as an internal standard molecule to correct the signal fluctuation of UA detection. The results show that the SERS method owns a linear response with a ranging from 5 × 10^-6 to 10^-3 M of UA characteristic peak of both 693 cm^-1 and 493 cm^-1 with a determination coefficient (R²) of 0.9878 and 0.9649, respectively. Additionally, the SERS sensor has been further used for the analysis of UA in sweat and good recoveries were obtained for the sensing of sweat. We believe that the developed SERS substrate has potential for applications in healthcare monitoring.

A new spectrophotometric method for uric acid detection based on copper doped mimic peroxidase

Cascade reactions catalyzed by natural uricase and mimic peroxidase (MPOD) have been applied for uric acid (UA) detection. However, the optimal catalytic activity of MPOD is mostly in acidic conditions (pH 2-5), mismatching the optimal catalytic alkaline environment of uricase. In this paper, using CuSO₄ and urea as raw materials, a MPOD with high catalytic activity in alkaline environment was synthesized by hydrothermal method. Then, based on coupling reaction of uricase/UA/MPOD/guaiacol (GA) system, a novel spectrophotometric method was established to detect 5-60 μmol/L UA (limit of detection = 3.14 μmol/L (S/N = 3)) and accurately quantified serum UA (275.6 ± 39.9 μmol/L, n = 5) with 95-105% of standard addition recovery. The results were consistent with commercial UA kit (p > 0.05). The MPOD could replace natural POD to reduce the cost of UA detection due to simple preparation and cheap raw materials, and is expected to achieve the specific detection of some substances, like glucose and cholesterol, combined with glucose oxidase and cholesterol oxidase.

Dual-emission fluorescence detection of histidine using carbon dots and calcein/Ni2+ complexes

Histidine (His) is a natural amino acid that plays very important roles in biota. However, the low concentrations of His in biological fluids and the similar structures and properties of other amino acids mean it is difficult to selectively determine His concentrations in biological fluids with a high degree of sensitivity. A novel ratiometric fluorescence probe for detecting His in aqueous solutions is described here. The method involves carbon dots (CDs) and calcein/Ni²⁺ complexes. At an excitation wavelength of 480 nm, the CD/calcein system emits green fluorescence (maximum emission from calcein at 512 nm) and red fluorescence (maximum emission from CDs at 617 nm). The presence of Ni²⁺ decreases the calcein fluorescence intensity because of static quenching caused by the formation of calcein/Ni²⁺ complexes but the CD fluorescence intensity remains almost unchanged. Fluorescence of calcein/Ni²⁺ complexes provides the response, and the presence of His binds to Ni²⁺ via cooperative chelation and produces free calcein causing fluorescence to be recovered. CDs provide a self-calibration fluorescence signal, the intensity of which remains almost unchanged in the presence of His. The ratio of the fluorescence intensities at 512 and 617 nm (I₅₁₂/I₆₁₇) was strongly related to the His concentration in the range 0.5-22 μM, and the detection limit was 0.16 μM. The specificity of Ni²⁺/His interactions allows His to be determined without interference from other species. The method was successfully used to determine His in diluted human urine. The recovery was acceptable, suggesting that the biosensor can be used to determine His in real samples.

Sophorajaponica L. flower mediated carbon dots with nitrogen and sulfur co-doped as a sensitive fluorescent probe for amoxicillin detection

This article first reported the green synthesis of N, S co-doped fluorescent carbon dots (N, S-CDs-Sop) and sought to establish the fluorescence detection system for amoxicillin (AMX). By using Sophorajaponica L. flower as the green precursor and dl-homocystine as the co-dopant, N, S-CDs-Sop were successfully prepared via a one-pot hydrothermal method, exhibiting good water solubility and excellent photoluminescence. It was revealed that the surface of N, S-CDs-Sop was abundant in amino, hydroxyl and carboxyl groups after being characterized by a variety of techniques. When Fe³⁺ was added, Fe³⁺ could be complexed with N, S-CDs-Sop to from N, S-CDs-Sop-Fe³⁺ chelation leading to a significant static quenching of fluorescence. However, when N, S-CDs-Sop, Fe³⁺ and AMX coexisted, AMX would coordinate with Fe³⁺ and form the strong chelate due to the favorable chemical structure, resulting in the rapid fluorescence recovery. Such a fast, simple and sensitive fluorescence "off-on" strategy with a low LOD and a relatively wide range was successfully applied to the detection of AMX, which is closely correlated with human health.

A Label-Free Fluorescent Sensor Based on Si,N-Codoped Carbon Quantum Dots with Enhanced Sensitivity for the Determination of Cr(VI)

A signal shut-off probe of Si, N-codoped carbon quantum dots (Si, N-CQDs) was exploited to detect Cr(VI) by fluorescence quenching without the aid of any biomolecules or labeling materials. The sensing system prepared the precursor of diacetone acrylamide and the silane coupling agent 3-aminopropyltriethoxysilane (KH-550) by a simple hydrothermal method, and the quantum yield is as high as 75% Si, N-CQDs. The fluorescence stability and microstructure of the Si, N-CQDs were studied. The Si, N-CQDs has a high sensitivity for detecting Cr(VI) with the linear range of 0–200 μM and the detection limit of 0.995 μM. The quenching mechanism of Si, N-CQDs is attributed to FRET.

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.

Recent developments on carbon dots-based green analytical methods: New opportunities in fluorescence assay of pesticides, drugs and biomolecules

Fluorescent carbon dots (CDs) grabs huge attention in analytical and bioanalytical applications due to their high selectivity towards target analyte, specificity, photostability, and quantum yield. Cost-effective and biocompatible properties of...