Dual recognition strategy for selective fluorescent detection of dopamine and antioxidants based on graphite carbon nitride in human blood serum

3-aminophenylboronic acid modified carbon nitride quantum dots as fluorescent probe for selective detection of dopamine and cell imaging

Dopamine (DA) is the most abundant catecholamine neurotransmitter in the brain and plays an extremely essential role in the physiological activities of the living organism. There is a critical need for accurately and efficiently detecting DA levels in organisms in order to reflect physiological states. Carbon nitride quantum dots (C3N4) were, in recent years, used enormously as electrochemical and fluorescence probes for the detection of metal ions, biomarkers and other environmental or food impurities due to their unique advantageous optical and electronic properties. 3-Aminophenylboronic acid (3-APBA) can specifically combine with DA through an aggregation effect, providing an effective DA detection method. In this work, 3-APBA modified carbon nitride quantum dots (3-APBA-CNQDs) were synthesized from urea and sodium citrate. The structure, chemical composition and optical properties of 3-APBA-CNQDs were investigated by XRD, TEM, UV-visible, and FT-IR spectroscopy. The addition of DA could induce fluorescence quenching of 3-APBA-CNQDs possibly through the inner filter effect (IFE). 3-APBA-CNQDs shows better selectivity and sensitivity to DA than other interfering substances. By optimizing the experiment conditions, good linearity was obtained at 0.10-51μM DA with a low detection limit of 22.08 nM. More importantly, 3-APBA-CNQDs have been successfully applied for the detection of DA in human urine and blood samples as well as for bioimaging of intracellular DA. This study provides a promising novel method for the rapid detection of DA in real biological samples.

Preparation of carbon quantum dot fluorescent probe from waste fruit peel and its use for the detection of dopamine

Carbon quantum dots (CQDs), as a new type of fluorescent nanomaterial, are widely used in the detection of small molecules. Abnormal dopamine secretion can lead to diseases such as Parkinson's disease and schizophrenia. Therefore, it is highly significant to detect dopamine levels in the human body. Using discarded fruit peels to prepare carbon quantum dots can achieve the reuse of kitchen waste, reduce pollution, and create value. Nitrogen-doped carbon quantum dots (N-CQDs) were prepared using the hydrothermal method, with orange peel as the raw material. The fluorescence quantum yield of N-CQDs reached a high value of 35.37% after optimizing the temperature, reaction time, and ethylenediamine dosage. N-CQDs were characterized using various techniques, including ultraviolet visible (UV-vis) spectroscopy, fluorescence spectrophotometer (PL), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR). These analyses confirmed the successful doping of nitrogen in the CQDs. The DA concentration ranged from 0 to 300 μmol L-1, and the linear equation for fluorescence quenching of N-CQDs was F/F0 = -0.0056c + 0.98647, with an R2 value of 0.99071. The detection limit was 0.168 μmol L-1. The recovery and precision of dopamine in rabbit serum were 98% to 103% and 2% to 6%, respectively. The prepared N-CQDs could be used as a fluorescent probe to effectively detect DA.

A label-free fluorescent sensor for rapid and sensitive detection of ctDNA based on fluorescent PDA nanoparticles

Technological advances in the detection of circulating tumor DNA (ctDNA) have made new options available for diagnosis, classification, biological studies, and treatment selection. However, effective and practical methods for analyzing this emerging class of biomarkers are still lacking. In this work, a fluorescent biosensor was designed for the label-free detection of ctDNA (EGFR 19 del for non-small cell lung cancer, NSCLC). The biosensor was based on the fact that MnO2 nanosheets (MnO2 NSs) have stronger affinity towards single-stranded DNA (ssDNA), as compared with double-stranded DNA (dsDNA). As a high-performance nanoenzyme, MnO2 NSs could oxidize dopamine (DA) into fluorescent polydopamine nanoparticles (FL-PDA NPs), which could be used as a fluorescence signal. The probe ssDNA could be adsorbed on the surface of MnO2 NSs through π-π stacking, and the active site would be masked, causing a lower fluorescence. After the targets were recognized by probe ssDNA to form dsDNA, its affinity for MnO2 NSs decreased and the active site recovered, causing a restored fluorescence. It was verified that Mn ions, •OH radicals and electron transfer were the important factors in the catalytic oxidation of DA. Under the optimal experimental conditions, this biosensor exhibited a detection limit of 380 pM and a linear range of 25-125 nM, providing reliable readout in a short time (45 min). This sensor exhibited outstanding specificity, stability and reproducibility. In addition, this sensor was applied to the detection of ctDNA in serum samples and cell lysates. It is demonstrated that FL-PDA NPs can be used as a fluorescence signal for easy, rapid and label-free detection of ctDNA without any other amplification strategies, and the proposed strategy has great potential for biomarker detection in the field of liquid biopsy.

A Paper-Based Biomimetic Sensing Device for the Discrimination of Original and Fraudulent Cigarette Brands Using Mixtures of MoS2 Quantum Dots and Organic Dyes

In this study, we investigated the combined effects of MoS₂ QDs' catalytic properties and the colorimetric responses of organic reagents to create a sniffing device based on the sensor array concept of the mammalian olfactory system. The aim was to differentiate the volatile organic compounds (VOCs) present in cigarette smoke. The designed optical nose device was utilized for the classification of various cigarette VOCs. Unsupervised Principal Component Analysis (PCA) and supervised Linear Discriminant Analysis (LDA) methods were employed for data analysis. The LDA analysis showed promising results, with 100% accuracy in both training and cross-validation. To validate the sensor's performance, we assessed its ability to discriminate between five cigarette brands, achieving 100% accuracy in the training set and 82% in the cross-validation set. Additionally, we focused on studying four popular Iranian cigarette brands (Bahman Kootah, Omega, Montana Gold, and Williams), including fraudulent samples. Impressively, the developed sensor array achieved a perfect 100% accuracy in distinguishing these brands and detecting fraud. We further analyzed a total of 126 cigarette samples, including both original and fraudulent ones, using LDA with a matrix size of (126 × 27). The resulting LDA model demonstrated an accuracy of 98%. Our proposed analytical procedure is characterized by its efficiency, affordability, user-friendliness, and reliability. The selectivity exhibited by the developed sensor array positions it as a valuable tool for differentiating between original and counterfeit cigarettes, thus aiding in border control efforts worldwide.

Controllable formation of polydopamine on carbon dots for ultrasensitive detection of alkaline phosphatase and ratiometric fluorescence immunoassay of benzocaine

Sensing alkaline phosphatase (ALP) activity with high sensitivity and accuracy is critical for both ALP-related health and food safety supervision and the development of ALP-triggered immunoassay platforms. Herein, an ultrasensitive ratiometric fluorescence (RF) sensing system based on the controllable formation of luminescent polydopamine and efficient quenching of carbon dots was proposed for the ALP activity assay, achieving quantitative detection in the range of 0.01-100 mU/L. Furthermore, this RF sensing system was integrated with an ALP-based ELISA platform to construct an RF-ELISA for benzocaine, a potentially abused anesthetic in edible fish, and ultrasensitive assay at the level of fg/mL was realized. This ratiometric strategy-based platform effectively shields various interferences through the self-calibration effect, thus providing more accurate and reliable quantification results. This study not only offers an efficient method for ultratrace detection of ALP and benzocaine but also proposes a universal platform for ultrasensitive detection of diverse targets in food analysis by replacing the recognition unit.

SERS determination of dopamine using metal-organic frameworks decorated with Ag/Au noble metal nanoparticle composite after azo derivatization with p-aminothiophenol

A specific surface-enhanced Raman scattering (SERS) assay for dopamine (DA) based on an azo derivatization reaction is proposed for the first time by preparation of p-aminothiophenol (PATP)-modified composite SERS substrate, composed of metal-organic framework (MIL-101) decorated with Au and Ag nanoparticles. As the result, the SERS method for detection of the azo reaction between PATP and DA exhibits superior sensitivity, selectivity, and stability. A reasonable linearity in the range 10^-6 to 10^-10 mol∙L^-1 is achieved, and the limit of detection is 1.2 × 10^-12 mol∙L^-1. The reactive SERS assay is free from interference in complex physiological fluid. The feasibility of the proposed SERS method for the detection of DA levels in fetal bovine serum (FBS) samples and human serum samples is validated by HPLC-MS methods, displaying promising application potential in early disease diagnosis.

Waste toner-derived micro-materials as low-cost magnetic solid-phase extraction adsorbent for the analysis of trace Pb in environmental and biological samples

Lead (Pb) is a toxic heavy metal and is commonly used in industrial applications. Thus, Pb poisoning is a concerning public health issue worldwide. The amounts of lead in natural water, urine, and blood can serve as significant indicators for monitoring the exposure of Pb poisoning. Waste toner has the characteristics of both "waste" and "resource," as it is a "resource in the wrong place." Here, a low-cost carboxylate-functionalized magnetic adsorbent was first synthesized from waste toner by a simple thermal treatment and served as a novel adsorbent with a flexible multidentate O-donor for pre-concentration of trace Pb. The characterization, adsorption behavior, and various factors of adsorption and desorption were adequately optimized, and prior to graphite furnace atomic absorption spectrometry (GFAAS) detection, a new magnetic solid-phase extraction method was proposed for the analysis of Pb in real environmental water and biological samples. The developed method exhibited a low detection limit (0.003 μg L^-1), high enrichment factor (88.6-fold), good linearity (0.01-0.3 μg L^-1), satisfactory precision with relative standard deviations of 7.9% (n = 7, C_Pb = 0.02 μg L^-1), fast adsorption kinetics (5 min), and strong ability to overcome matrix interference. Validation was also performed by analyzing a certified standard reference material, and the method was successfully applied to real tap water, lake water, human urine, and human blood serum with satisfactory recoveries of 92.6-109%.