Inner filter effect (IFE) as a simple and selective sensing platform for detection of tetracycline using milk-based nitrogen-doped carbon nanodots as fluorescence probe

A simple, selective, and sensitive turn-off fluorescent assay for detecting of tetracycline in pharmaceutical dosage form based on inner filter effect (IFE) sensing platform has been described. In this IFE sensing strategy, N-doped carbon dots (CDs) were prepared by one-pot solvothermal synthesis using milk as a precursor and were directly used as a fluorophore in IFE. The prepared CDs were characterized by common spectroscopic and microscopic techniques. The CDs exhibited excitation-wavelength dependent emission with 10% as the fluorescence quantum yield. The fluorescence of CDs was decreased in correlation to the addition of absorber (tetracycline), as the excitation spectrum of the fluorophore (CDs) matches the absorption spectrum of the absorber. The present IFE-based sensing platform showed a good linear relationship from 2.0 µM to 200 µM (R² = 0.9960) and provided a detection limit of 0.6 µM (signal-to-noise ratio of 3). Additionally, the cytotoxic effects of CDs were determined using normal healthy male Balb/C mice model treated with various doses of CDs and at the end of the study, no mortality or even no sign of toxicity was observed at oral doses of 100 and 200 mg/kg CDs in all treated animals. The proposed nanoprobe assay is a free from interferences, low-cost, biocompatible, and accurate for the detection of tetracycline in pharmaceutical formulation.     

Direct and single-step sensing of primary ovarian cancers related glycosidases

High sensitive, accurate detection for tumor-associated overexpressed enzyme activity is highly significant for further understanding enzyme function, discovering potential drugs, and early diagnosis and prevention of diseases. In this work, we developed a facile, direct and single-step detection platform for primary ovarian cancers related glycosidase activity based on the inner filter effect(IFE) between glycosidase catalytic product and black phosphorus quantum dots(BPQDs). Highly fluorescent BPQDs were successfully synthesized from bulk black phosphorus by a simple liquid exfoliation method. Under the catalysis of β-galactosidase, p-nitrophenyl-β-D-galactopyranoside(PNPG) was transformed into pnitrophenol(PNP) and β-D-galactopyranoside. Meanwhile, the absorption of catalytic product PNP greatly overlapped with the excitation and emission spectra of fluorescent BPQDs, leading to the fluorescence quenching of BPQDs with a high quenching efficiency. The proposed sensing strategy provided a low detection limit of 0.76 U/L, which was 1 — 2 orders of magnitude lower than most unmodified sensing platforms. D-Galactal was selected as the inhibitor for β-galactosidase to further assess the feasibility of screening potential inhibitors. The fluorescence recovery of BPQDs suggests that the unmodified sensing platform is feasible to discover potential drugs of β-galactosidase. Our work paves a general way in the detection of glycosidase activity with fluorescent BPQDs, which can be promising for glycosidase-related disease diagnosis and pathophysiology elucidation.     

A Smartphone-assisted Paper-based Analytical Device for Fluorescence Assay of Hg2+

Rapid, efficiency and portable detection systems in low-resource settings with limited laboratory equipment and technical expertise are urgently needed. Herein, an integrated platform composed of a paper-based analytical device and a smartphone detection system for Hg²⁺ onsite testing was developed. Nitrogen-doped carbon dots(N-CDs) were synthesized by a simple hydrothermal method using citric acid as the carbon source and ethanediamine as the nitrogen source, which gave out bright blue fluorescence under the excitation at 350 nm UV light and the absolute fluorescence quantum yield was 17.1%. The fluorescence of the prepared N-CDs can be effectively quenched by Hg²⁺. In addition, an external attachment of smartphone for illumination and external light interference was designed to trace the fluorescence signals, and a software application of Android system with simple operation program was developed to perform snapshot and image processing. The smartphone-assisted detection system was combined with the N-CDs decorated paper chip to achieve the sensitive detection of Hg²⁺ in water samples. This integrated method for reliable sensing of Hg²⁺ shows a good linear detection range of 10-800 μmol/L(R²=0.9595) with detection limit of 1.07×10^-8 mol/L.     

基于内滤效应的信号增强型诺氟沙星荧光分析法

基于茜素红和卟啉之间的荧光内滤效应,成功构建了一种分子识别事件与信号报告空间分离的、高选择性的荧光增强型诺氟沙星分析方法。结果表明,无诺氟沙星时,茜素红在420 nm处有最大吸收,这和卟啉的最大激发波长有较大重叠,茜素红和卟啉之间因发生内滤效应导致卟啉的荧光被有效猝灭;而茜素红与诺氟沙星的配合物在523 nm处有最大吸收,和卟啉的最大激发波长不再重叠,即诺氟沙星与茜素红之间的荷移反应破坏了该内滤效应,导致卟啉荧光恢复,据此,可将茜素红的吸收信号转变为高灵敏的卟啉的荧光信号。在最佳实验条件下,诺氟沙星的质量浓度在10 ~ 450 mg?L-1范围内与体系的相对荧光强度(IF/I0F)呈线性关系(r2=0.987 8),检出限(S/N=3)为5 mg?L-1。方法选择性好,常见金属离子和药物辅料不干扰诺氟沙星的测定。该研究利用内滤效应,将灵敏度较低的诺氟沙星紫外可见分析法转换为灵敏度较高的荧光分析法,且无需将分子识别单元和信号转导单元共价连接,无需复杂的荧光探针合成工艺,为设计该类药物的荧光分析法提供了新思路。     

Aptamer-Based Fluorescence Nanoprobe for Sensitive and Selective Detection of Potassium

A new aptamer-based fluorescence nanoprobe for potassium ion (K⁺) has been developed. The nanoprobe employs gold nanoparticles (AuNPs) as the sensing platform and Rhodamine B as the fluorescence indicator. Aptamer acts as the switch of fluorescence signal of Rhodamine B. In the presence of K⁺, aptamer departs from AuNPs as a result of the formation of G-quartets with K⁺, leading to the decrease of fluorescence signals. Under the optimum conditions, the limit of detection (LOD) for K⁺ is as low as 3.8 nM. The proposed method was successfully applied in the determination of K⁺ in human saliva sample.     

Homogeneous fluorescence-based immunoassay via inner filter effect of gold nanoparticles on fluorescence of CdTe quantum dots

Homogeneous immunoassays are becoming more and more attractive for modern medical diagnosis because they are superior to heterogeneous immunoassays in sample and reagent consumption, analysis time, portability and disposability. Herein, a universal platform for homogeneous immunoassay, using human immunoglobulin (IgG) as a model analyte, has been developed. This assay relies upon the inner filter effect (IFE) of gold nanoparticles (AuNPs) on CdTe QDs fluorescence. The immunoreaction of antigen and antibody can induce the aggregation of antibody-functionalized AuNPs, and after aggregation the IFE of AuNPs on CdTe QDs fluorescence is greatly enhanced, resulting in a decrease of fluorescence intensity in the system. Based on this phenomenon, a wide dynamic range of 1-100 pg mL(-1) for determination of IgG can be obtained. The proposed method shows a detection limit of 0.3 pg mL(-1) for human IgG, which is much lower than the corresponding absorbance-based approach and compares favorably with other reported fluorescent methods. This immunoassay method is simple, rapid, cheap, and sensitive. The proposed method has been successfully applied to measuring IgG in serum samples, and the obtained results agreed well with those of the enzyme-linked immunosorbent assay (ELISA).     

Switch-on fluorescence sensor for ascorbic acid detection based on MoS2 quantum dots-MnO2 nanosheets system and its application in fruit samples

In this work,molybdenum disulfide quantum dots(MoS_2 QDs) were firstly prepared by hydrothermal method using sodium molybdate and glutathione as precursors,and applied in ascorbic acid detection.When joining MnO_2 nanosheets into MoS_2 QDs solution,they produced an obvious fluorescence quenching,which should be due to inner filter effect(IFE).Meanwhile,the fluorescent probe was formed,Interestingly,we found that this quenching phenomenon disappeared with the addition of ascorbic acid,In other words,the fluorescence gradually restored.This recovery phenomenon is mainly due to the reduction effect of ascorbic acid for MnO_2 nanosheets.Under the optimum conditions,the limit of detection(LOD) of 39 nmol/L for ascorbic acid was achieved with a linear range of 0.33-5.00 μmol/L.The repeatability was better than 5.0% for ascorbic acid in both standard and fruit samples(n = 3).Moreover,the as-fabricated fluorescent sensing system was successfully employed to detect the ascorbic acid levels in hawthorn and jujube with satisfactory results.     

Fluorescent blood glucose monitor by hemin-functionalized graphene quantum dots based sensing system

In the present work, a highly sensitive and specific fluorescent biosensor for blood glucose monitoring is developed based on hemin-functionalized graphene quantum dots (GQDs) and glucose oxidase (GOx) system. The GQDs which are simply prepared by pyrolyzing citric acid exhibit strong fluorescence and good water-solubility. Due to the noncovalent assembly between hemin and GQDs, the addition of hemin can make hydrogen peroxide (H₂O₂) to destroy the passivated surface of GQDs, leading to significant fluorescence quenching of GQDs. Based on this effect, a novel fluorescent platform is proposed for the sensing of glucose. Under the optimized conditions, the linear range of glucose is from 9 to 300 μM, and the limit of detection is 0.1 μM. As unique properties of GQDs, the proposed biosensor is green, simple, cost-efficient, and it is successfully applied to the determination of glucose in human serum. In addition, the proposed method provides a new pathway to further design the biosensors based on the assembly of GQDs with hemin for detection of biomolecules.     

Quantitative analysis of multiple urinary biomarkers of carcinoid tumors through gold-nanoparticle-assisted laser desorption/ionization time-of-flight mass spectrometry

A highly selective and sensitive coumarin-based chemodosimeter 1 for Cu(2+) in water is reported in this work. 1 was designed and facilely synthesized by a one-step reaction with coumarin as a fluorophore and 2-picolinic acid as the binding moiety, which showed very week fluorescence in buffer solution, and its fluorescence was considerably enhanced by the addition of Cu(2+) at room temperature in 5 min. Mechanism study suggested that Cu(2+) promoted the hydrolysis of 1 via the catalytic sensing cycle, generating a highly fluorescent product 7-hydroxycoumarin with fluorescence signal greatly amplified. The probe exhibited remarkably selective fluorescence enhancement to Cu(2+) over other metal ions at 454 nm, with a detection limit of 35 nM Cu(2+). Under optimal condition, 1 was successfully used for the determination of Cu(2+) in fetal equine serum and two water samples.     

Application of 3,4,9,10-perylenetetracarboxylic diimide microfibers as a fluorescent sensing platform for biomolecular detection

In this paper, we report on the use of 3,4,9,10-perylenetetracarboxylic diimide microfibers (PDIMs) as an effective fluorescent sensing platform for DNA detection for the first time. This sensing system exhibits a detection limit as low as 15 nmol L⁻¹ and has a high selectivity down to single-base mismatch. The general concept used in this approach is based on adsorption of fluorescently labeled single-stranded DNA (ssDNA) probe by PDIM due to the strong π–π stacking between unpaired DNA bases and PDIM. As a result, the fluorophore is brought into close proximity of PDIM, leading to substantial fluorescence quenching. In the presence of the target, the specific hybridization of the probe with its complementary DNA sequence generates a double stranded DNA (dsDNA) which detaches from PDIM, leading to fluorescence recovery. Its generality of this sensing platform for protein detection is also demonstrated.     

A ratiometric fluorescent probe based on boron dipyrromethene and rhodamine Förster resonance energy transfer platform for hypochlorous acid and its application in living cells

We have developed a ratiometric fluorescent probe BRT based on boron dipyrromethene (BODIPY) and rhodamine-thiohydrazide Förster resonance energy transfer (FRET) platform for sensing hypochlorous acid (HOCl) with high selectivity and sensitivity. The probe can detect HOCl in 15 s with the detection limit of 38 nM. Upon mixing with HOCl the fluorescence colour of probe BRT changed from green to orange. Moreover, probe BRT was applied to successfully monitor HOCl in living RAW 264.7 cells.     

A smartphone metabolomics platform and its application to the assessment of cisplatin-induced kidney toxicity

The application of smartphones to medical devices has been gaining attention in addressing accessibility and cost issues in healthcare, and the detection of medically relevant compounds has been demonstrated using customized smartphone hardware and/or software. Metabolomics, a newly rising omics field, has also spawned many medical applications but requires highly sophisticated and expensive equipment. Here, we describe a portable smartphone platform, built with readily available and affordable materials, that can perform all of the critical aspects of metabolomics. Excluding the smartphone itself, the total materials for the platform were obtained at less than US $20. For spectral data acquisition, the system utilized visible light (400–700 nm) and a built-in camera. All of the data processing, statistical analysis, and final-visualization components necessary for decision making were implemented in the smartphone platform. The platform is generally applicable as long as the analytes absorb visible light. We provide a proof-of-concept example wherein the metabolomics platform was applied to the assessment of cisplatin-induced kidney toxicity in a rat model, correctly predicting 7 out of 8 test samples.     

Facile synthesis of tomato-based carbon nanodots and its utilization in sensitive detection of tartrazine

Carbon nanodots (CDs) with superior fluorescence performance were obtained by hydrothermal method using tomatoes as raw materials. When the ultraviolet absorption band of tartrazine and the fluorescence spectrum of CDs have complementary overlaps, the fluorescent internal filter effect (IFE) occurred. Furthermore, the degree of quenching of fluorescence intensity of CDs has an excellent linear correlation with tartrazine concentration. And based on this principle, a method for detecting tartrazine was established. As the decrease of fluorescence intensity, tartrazine can be measured in the linear range of 0.1 μM–40 μM. The detection limit is 39 nM, and the recovery rate is 90.7%～114.5%. The established protocol was also effectively employed to assay tartrazine in beverage samples, indicating that it has great potential for food color analysis.     

胞苷保护的铜纳米簇新型荧光探针检测重铬酸根离子

基于重铬酸根离子(Cr_2O_7~(2-))对胞苷保护的荧光铜纳米簇(Cu NCs)的猝灭作用,构建了一种可用于检测Cr_2O_7~(2-)的荧光传感器.实验结果表明,该传感体系检测Cr_2O_7~(2-)的线性范围为0.05~7.0μmol/L,检出限为24 nmol/L(S/N=3).该传感器对Cr_2O_7~(2-)的检测具有良好的选择性,可用于湖水样中Cr_2O_7~(2-)的检测.     

A new coumarin-based fluorescence turn-on chemodosimeter for Cu in water

A highly selective and sensitive coumarin-based chemodosimeter 1 for Cu²⁺ in water is reported in this work. 1 was designed and facilely synthesized by a one-step reaction with coumarin as a fluorophore and 2-picolinic acid as the binding moiety, which showed very week fluorescence in buffer solution, and its fluorescence was considerably enhanced by the addition of Cu²⁺ at room temperature in 5 min. Mechanism study suggested that Cu²⁺ promoted the hydrolysis of 1 via the catalytic sensing cycle, generating a highly fluorescent product 7-hydroxycoumarin with fluorescence signal greatly amplified. The probe exhibited remarkably selective fluorescence enhancement to Cu²⁺ over other metal ions at 454 nm, with a detection limit of 35 nM Cu²⁺. Under optimal condition, 1 was successfully used for the determination of Cu²⁺ in fetal equine serum and two water samples.     

Time-resolved fluorescence aptamer-based sandwich assay for thrombin detection

In the present study, the authors report a novel sensitive method for the detection of thrombin using time-resolved fluorescence sensing platform based on two different thrombin aptamers. The thrombin 15-mer aptamer as a capture probe was covalently attached to the surface of glass slide, and the thrombin 29-mer aptamer was fluorescently labeled as a detection probe. A bifunctional europium complex was used as the fluorescent label. The introduction of thrombin triggers the two different thrombin aptamers and thrombin to form a sandwich structure. The fluorescence intensity is proportional to the thrombin concentration. The present sensing system could provide both a wide linear dynamic range and a low detection limit. The proposed sensing system also presented satisfactory specificity and selectivity. Results showed that thrombin was retained at the aptamer-modified glass surface while nonspecific proteins were removed by rinsing with buffer solution. This approach successfully showed the suitability of aptamers as low molecular weight receptors on glass slides for sensitive and specific protein detection.     

Jigsaw-like mini-pillar platform for multi-mode biosensing

The multiple sensing provides booming options to eliminate interference and ensure the accuracy of detection by mutually coupling and validating multiple data sets. Here, we integrate the jigsaw-like multifunctional mini-pillar platform to perform multi-mode (electrochemical, fluorescence, surface-enhanced Raman scattering (SERS) and colorimetric) sensing in individual microdroplets. Each mini-pillar connector can parallelize together by specific concave-convex interface to form integrated jigsaw-like platform for multi-mode sensing, and each specific mini-pillar can be modified into the individual sensing unit to read the prescribed signals. We successfully implemented electrochemical, fluorescence, SERS and colorimetric detection by multiple signals coupling to reduce the false positive analysis. Such platform brings a promising clue of in-situ analysis and point-of-care testing for disease diagnosis and health monitoring.     

Novel colorimetric,photothermal and up-conversion fluorescence triple-signal sensor for rosmarinic acid detection

Rosmarinic acid (RA) is promising as a natural and nontoxic food additive. However, many analysis methods for RA generally depend on large instruments and single signals for quantitative detection. A new up-conversion fluorescence, colorimetric and photothermal multi-modal sensing strategy is developed for the quantification of RA. β-cyclodextrin (CD) modified citric acid (Cit) wrapped NaYF₄:Yb/Er-Cit-CD (Y:Yb/Er-Cit-CD) up-conversion nanocomposite has been synthesized, which emits green fluorescence at 550 nm under 980 nm near-infrared (NIR) excitation. In the presence of oxidized 3,3′,5,5′-tetramethylbenzidine (oxTMB), the green fluorescence is significantly quenched attributed to the fluorescence inner filter effect (IFE) between oxTMB and Y:Yb/Er-Cit-CD. When RA is intervened, blue oxTMB is reduced to colorless 3,3′,5,5′-tetramethylbenzidine (TMB) inducing the recovery of up-conversion fluorescence. At the same time, colorimetric and photothermal signals readout can be easily achieved thanks to the color indication and photothermal effect of the oxTMB. The constructed Y:Yb/Er-Cit-CD/oxTMB sensor displays high sensitivity, visibility and simplicity for RA, and the limits of detection (LOD) for fluorescence, colorimetric and photothermal were 0.004 µmol/L, 0.036 µmol/L and 0.043 µmol/L, respectively. This sensing system is successfully performed for the detection of RA in food samples.     

Rationally designed meso-benzimidazole-pyronin with emission wavelength beyond 700 nm enabling in vivo visualization of acute-liver-injury-induced peroxynitrite

Fluorescent dyes with fluorescence emission above 700 nm are favorable for bio-imaging due to the higher tissue transparency and lower background fluorescence. In this study, we present a meso-benzimidazole-pyronin platform (SiBMs) with fluorescence emission maxima above 700 nm, which possess good cell permeability, photostability, and lysosomal localization. The great photophysical properties of the SiBMs encouraged us to further exploit their application toward bio-imaging. We synthesized the reduced ‘dihydro’ derivative HSiBM3 for sensing ONOO^?, with high selectivity and sensitivity and a fast fluorescence “off-on” response (within 2 s). Then, we confirmed the potential of HSiBM3 for visualizing exogenous and endogenous ONOO^? in cells and mice. More importantly, HSiBM3 was successfully employed for visualizing acute-liver-injury-induced peroxynitrite.