A Portable Smartphone Platform Using a Ratiometric Fluorescent Paper Strip for Visual Quantitative Sensing

Molecularly Imprinted Ratiometric Fluorescence Nanosensors

Molecularly imprinted ratiometric fluorescence (MIR-FL) nanosensors feature recognition selectivity, detection sensitivity, application universality, visualization accuracy, and device portability, and have gained popularity. However, the fluorescence intensity, nanostructure, color range, and practical application of the sensor still face severe difficulties to be solved. New strategies combined with various technologies have been developed to construct MIR-FL nanosensors for expanded applications. This Perspective highlights current resarch challenges and future prospects involving constructions and applications of MIR-FL nanosensors including dual-emission and triple-emission modes. The postimprinting mixing/modification strategies, microdevices, and multitarget detection are focused, and technology synergy, sensitivity/reproducibility improvement, application diversity/portability, etc. are proposed.

Comparative and Selective Interaction of Amino Acid d-Cysteine with Colloidal Gold Nanoparticles in the Presence of a Fluorescent Probe in Aqueous Medium

In this communication, we report the comparative and selective interaction of amino acid d-cysteine (d-Cys) with citrate caped gold nanoparticles (Au NPs) in the presence of a fluorescent dye, rhodamine B (RhB), in aqueous solution. Au NPs of size 27.5 nm could almost fully quench the steady-state fluorescence emission of RhB at their optimum concentrations in the mixed solution. The interactions of d-Cys, l-Cys, all other relevant d- and l-amino acids, neurotransmitters, and other relevant biological compounds with the Au NPs/RhB mixed solution have been explored by monitoring the fluorescence recovery efficiencies from the almost fully quenched state of RhB fluorescence via a simple steady-state spectrofluorometric method. The higher fluorescence recovery for the interaction of d-Cys with the Au NPs/RhB mixed system is accompanied by a distinct color change (red-wine to bluish-black) of the assay medium after the reaction compared to that of all other interfering compounds considered in this work. The sensitivity of this fluorometric response lies in a broad linear range of concentrations of d-Cys and the limit of detection (LOD) is found to be 4.2 nM, which is low compared to many other methods available in the literature. The different degrees of interaction of d-Cys and l-Cys with the Au NPs/RhB mixed sample have been further explored by circular dichroism (CD) spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The selective interaction of d-Cys with the proposed Au NPs/RhB mixed system is also found to be correlated with interparticle cross-linking and aggregations of nanoparticles by the analysis of ζ potential and dynamic light scattering (DLS) study, transmission electron microscopy (TEM), atomic force microscopy (AFM), UV-vis absorption spectroscopy etc. The proposed interaction mechanism is further studied with a normal human urine sample to elucidate that the optimized combination of Au NPs and RhB may be realized as an efficient platform for detection of the amino acid d-Cys in a real biosample via a simple fluorometric approach.

Enzyme-free and rapid visual quantitative detection for pesticide residues utilizing portable smartphone integrated paper sensor

Serious toxicity for organisms from pesticide glyphosate (Gly) residues to the ecosystem and human health has become a consensus. Rapid and selective detection of glyphosate, especially using a simple and portable instrument, is highly desired. In this work, we develop a novel enzyme-free rapid and visual ratiometric fluorescence sensor for selectively quantitative detecting glyphosate by integrating the designed blue carbon nanodots (CDs) and gold nanoclusters (Au NCs). The fluorescence of CDs can be quickly quenched via aggregation-caused quenching (ACQ) within 2 s after introducing glyphosate, resulting from the formation of CDs-Gly-CDs complex aggregation. While the Au NCs serve as the reference signal without any change, therefore leading to obvious and instant ratiometric fluorescence variation from blue to pink to orange. The broad linear range was obtained from 0 to 180 nM with a satisfactory detection limit of 4.19 nM. Furthermore, this approach was successfully applied to detect glyphosate in real samples and a portable smartphone platform integrated paper sensor was developed for in-site visual quantitative glyphosate detection, offering a promising strategy for the construction of enzyme-free trace hazard detection system.

Reversible fluorescent test strip with red fluorescent carbon dots for monitoring water in organic solvents: Visual detection via a smartphone

Herein, a novel type of red-emitting carbon dots called TN-CDs was created via a one-step hydrothermal approach using neutral red and tartaric acid as raw materials. The fluorescence of TN-CDs was gradually quenched as the amount of water increased, and the color of the solution changed from yellow to pink mauve (or purple to pink). The reaction could be completed within only 5 s in various organic solvents such as N,N-Dimethylformamide (DMF), methanol (MeOH), acetonitrile (ACN), and ethanol (EtOH) with linear detection ranges of 1.2%-35.0%, 0.5%-20.0%, 0.25%-5.0% and 0%-16.0%, respectively. In addition, we prepared a reusable test strip and then combined it with TN-CDs to detect water content in DMF, as well as integrated it with smartphone software, a UV lamp, and a dark chamber for real-time, on-site, visual quantitative detection of the water content.

Double Signal Amplification Strategy for Dual-Analyte Fluorescent Aptasensors for Visualizing Cancer Biomarker Proteins

The simultaneous analysis of diversified biomarkers with high sensitivity and in a point-of-care (POC) manner is of great significance for facile and early cancer diagnosis. Herein, we develop a target amplification-assisted ratiometric fluorescence assay (TARFA) platform integrating the dual-amplification strategy and colorimetric readout technology for sensitive and specific detection of two malignancy-associated biomarkers. Meanwhile, the NIR-excited alkaline-earth sulfide nanodots (ASNDs) with an ultrasmall (<10 nm) diameter and tunable emission wavelength are employed to replace commonly UV/visible light-excited fluorescent labels to minimize background interference from the sample matrix. Unique advantages of the ASNDs, together with superiority of consecutive signal amplification of enzymatic target recycling (ETR) and hybridization chain reaction (HCR), realize the pg/mL-range detection limit in specifically recognizing the vascular endothelial growth factor (VEGF) and soluble interleukin-6 receptors (sIL-6R). The combination detection of the dual analyte exhibits an improved sensitivity for cancer diagnosis. The addition of the target biomarkers leads to an increasingly ratiometric RGB signal, and quantification based on the ratio-dependent signal is more reliable rather than measuring the absolute RGB signals. Moreover, perceptible color transformation makes the TARFA platform competent for visual analysis of the target analytes as convenient as reading the pH indicator strip, and hue-based image analysis also improves the method with fine precision by quantitatively identifying the visual color. This work provides a new kind of NIR-excited aptasensing platform with a low detection limit, high throughput, and great portability, which also highlights the potential of the ASNDs in biomolecular fluorescent labeling.

Phone Camera Nano-Biosensor Using Mighty Sensitive Transparent Reusable Upconversion Paper

Lycopene, a natural colorant and antioxidant with a huge growing market, is highly susceptible to photo/thermal degradation, which demands real-time sensors. Hence, here a transparent upconversion nanoparticles (UCNPs) strip having 30 mol % Yb, 0.1 mol % Tm, and β-NaYF4 UCNPs, which shows an intense emission at 475 nm, has been developed. This strip has been found to be sensitive to lycopene with a detection limit as low as 10 nM using a smartphone camera, which is due to static quenching that is confirmed by the lifetime study. In comparison to previous paper strips, here the transparent strip has minimal scattering with maximum sensitivity in spite of not using any metal quenchers. An increase in strip hydrophobicity during the fabrication process complements the strip to selectively permeate and present an extraction-free substitute analysis for chromatography. Hydrophobicity endows the strip with the capability to reuse the strip with ∼100% luminescence recovery.

Ultrathin 2D Eu3+@Zn-MOF Nanosheets: A Functional Nanoplatform for Highly Selective, Sensitive, and Visualized Detection of Organochlorine Pesticides in a Water Environment

Facile and rapid detection of residual organic pesticides on the fruits and vegetables has recently drawn increased attention in the food safety field. Herein, a surfactant-assisted solvothermal route with subsequent post-modification was designed for the preparation of Eu³⁺-functionated Zn-BDC ultrathin nanosheets (labeled as Eu³⁺@Zn-MOF-NS, BDC: 1,4-benzenedicarboxylate) with the thickness of 5 nm. The as-obtained Eu³⁺@Zn-MOF-NS could be homogeneously dispersed in aqueous systems to form a highly-stable collosol. Under the UV excitation of 325 nm, the as-obtained Eu³⁺@Zn-MOF-NS displayed red photoluminescence emission of Eu³⁺ ions, which could be notably quenched by an organochlorine pesticide, 2,6-dichloro-4-nitroaniline (DCNA), without interferences from ions, organic small molecules, and other pesticides. The detection limit and K_sv were 0.17 μM (35 ppb) and 3.2 × 10⁵ M^-1 in the water system, respectively. Moreover, the present 2D Eu³⁺@Zn-MOF sensor was also employed for the detection of DCNA in Chaohu Lake water and tap water and in apple, cabbage, and pakchoi samples with the relative standard deviation (RSD) ranging from 4.74 to 9.77%. Further investigations revealed that the competitive absorption between DCNA and the as-obtained Eu³⁺@Zn-MOF-NS resulted in the fluorescence quenching of the probe.

A fluorescent probe based on POSS for facilitating the visualization of HClO and NO in living cells and zebrafish

The main production area of HClO and NO is the mitochondria and has modulatory effects on multiple human diseases. Simultaneous detection of signaling molecules such as HClO and NO is an important approach for exploring the complex relationship between HClO and NO in mitochondria. However, most probes can detect only one species or are unable to complete the monitoring of HClO and NO in the NIR channel. There are only few reports on reasonable tools that can simultaneously monitor the presence of HClO and NO in the NIR channel. In this work, to solve this difficulty, a POSS-assisted NIR fluorescent probe with dual-response was rationally devised and developed. The probe Mito-Cy possessed high specificity and responsiveness to HClO and NO in spectral experiments. Notably, the probe exhibited excellent responsiveness and sensitivity to HClO and NO in living cells and the zebrafish model.

Intelligently design primary aromatic amines derived carbon dots for optical dual-mode and smartphone imaging detection of nitrite based on specific diazo coupling

Primary aromatic amines derived carbon dots (PAA-CDs) with the protonated amino groups and high quantum yield of 46% were favorably obtained by one-step solvothermal treatment of m-phenylenediamine (m-PDA) in acidic environment. The interaction between the PAA-CDs and nitrite (NO₂^-) was inherited the characteristic reaction of m-PDA (a primary aromatic amine) and NO₂^-, resulting in strong fluorescence quenching and obvious absorption variation of the PAA-CDs. Meanwhile, a chromogenic reaction of diazo coupling can cause significant color changes. Hence, the PAA-CDs were developed for an optical dual-mode and smartphone imaging sensor for NO₂^- detection in the range of 3.0 ~ 40.0 μM with high selectivity, good sensitivity, and excellent anti-interference capability. A limit of detection (LOD) of 0.024 μM and 0.16 μM was implemented by fluorometry and colorimetry, respectively. For smartphone imaging colorimetry, the LODs of 0.46 μM (visible color) and 0.99 μM (fluorescence color) were acquired. More importantly, the established sensor has been successfully applied for the dynamic detection of NO₂^- in various food samples with the satisfying results. A smartphone imaging colorimetry method based on the CDs was firstly proposed to visually and quantitatively detect NO₂^-, which will broaden the application range of the CDs in food safety inspection.

A highly selective and sensitive ratiometric fluorescent probe for quantitative detection of Al(III) in different natural matrices

Highly selective and sensitive assay of Al(III) using ratiometric fluorescence enhancement is reported in an aqueous solution. The probe (named as RS5) exhibits a red-shift of 54 nm upon binding with Al(III) ion. The significant enhancement response of RS5 at 481 nm is attributed to the formation of a 1:1 complex between the probe and Al(III), wherein RS5 acts as a tridentate NNN-donor ligand. The complexation process is ascertained by 1H, 13C and 27Al NMR and HR-MS spectral techniques. The binding constant of the complex is determined to be 1.3x105 M-1. The ratiometric change in fluorescence upon complexation with Al(III) is ascribed to increase in intramolecular charge transfer (ICT) transition along with chelation enhanced fluorescence (CHEF) processes. The probe can be applied for monitoring Al(III) in a pH range of 6 - 8. The limit of detection (LOD) of RS5 for the examination of Al(III) is found to be 0.3 µM. With an aim to understand the sensing behaviour of RS5, the optical properties of the probe and its Al(III) complex are investigated using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. The probe is successfully employed for the determination of Al(III), with very high recovery percentages, in natural matrices like deep well water, tap water, drinking water, pond water, river water, bovine serum albumin (BSA) solution and blood serum.

Engineering of Portable Smartphone Integrated with Liposome-Encapsulated Curcumin for Onsite Visual Ratiometric Fluorescence Imaging of Hypochlorite

Precisely onsite monitoring of hypochlorite (ClO^- ) is of great significance to guide its rational use, reducing/avoiding its potential threat toward food safety and human health. Considering ClO^- could quench fluorescence of curcumin (CCM) by oxidizing the o-methoxyphenol of CCM into benzoquinone, a portable ratiometric fluorescence sensor integrated with smartphone was designed for realizing the visual point-of-care testing (POCT) of ClO^- . The amphiphilic phospholipid polymer was used as carrier to wrap curcumin, forming a novel liposome-encapsulated CCM, which provided a scaffold to bind with [Ru(bpy)₃ ]²⁺ through electrostatic interaction, thus assembling [Ru(bpy)₃ ]²⁺ -functionalized liposome-encapsulated CCM ([Ru(bpy)₃ ]²⁺ @CCM-NPs). Further integrated with smartphone, visual imaging of [Ru(bpy)₃ ]²⁺ @CCM-NPs could be achieved and the accurate onsite detection of ClO^- could be realized with a detection limit of 66.31 nM and a linear range of 0.2210 to 80.0 μM. In addition, the sensor could monitor ClO^- in real samples with an onsite detection time of ∼154.0 s.

A ratiometric fluorescence platform based on carbon dots for visual and rapid detection of copper(II) and fluoroquinolones

A simple smartphone-integrated ratiometric fluorescent sensing system for visual determination of copper ions (Cu²⁺) and fluoroquinolones (FQs) was developed based on carbon dots (CDs) which were synthesized through the high-temperature pyrolysis of citric acid. In this system, with the fluorescence resonance energy transfer effect between CDs and 2,3-diaminophenazine (oxOPD), the detection of Cu²⁺ and ciprofloxacin (CIP, an example for FQs) was realized. Cu²⁺ catalyzes the oxidation of OPD to form oxOPD with yellow fluorescence, resulting in the quenching of CDs. In addition, CIP can inhibit the catalytic activity of Cu²⁺ and induce the recovery of CDs fluorescence. Under the excitation of 400 nm, the changes of CDs fluorescence at 472 nm and oxOPD fluorescence at 556 nm were monitored. The detection results showed that the sensing system exhibited good selectivity and sensitivity to Cu²⁺ and CIP with the limit of detection of 2.32 × 10^-8 mol L^-1 and 0.2 ng mL^-1, respectively. In addition, a smartphone was developed as a portable analyzer to capture the change of fluorescence color and quickly analyze the concentration of Cu²⁺ and CIP. The proposed smartphone-based sensing platform has satisfactory sensitivity, and it has application prospects for detecting Cu²⁺ and FQs in food safety monitoring.

NIR-to-Vis Handheld Platforms for Detecting miRNA Level and Mutation Based on Sub-10 nm Sulfide Nanodots and HCR Amplification

Sub-10 nm monodisperse alkaline-earth sulfide nanodots (ASNDs) with bright near-infrared (NIR)-excitation fluorescence and adjustable emission wavelength were prepared by a thermal decomposition method for the first time. The ASNDs exhibited high NIR-to-vis conversion efficiency and served as multicolor fluorescent labels in the proposed miR-224 assay. Targeted detection of the miR-224 level and single-nucleotide variation in miR-224 was carried out on a smartphone-based platform using a hybridization chain reaction (HCR) amplification strategy. In the presence of miR-224, the ASND-labeled HCR probes self-assembled on the surface of the diagnosis kits, generating strong fluorescent signals linearly proportional to miR-224 contents in the range of 10-2000 fM. Significantly, mutations in miR-224 led to the variation in the fluorescence intensity ratio in RGB channels. Simultaneously, evident changes of fluorescent brightness and color were easily visualized by the naked eye, which enabled on-site discrimination of miR-224 with different mutant loci. This work provides a novel preparation approach for ultrasmall NIR excitation sulfide nanodots and reveals the potential of the as-synthesized ASNDs in point-of-care (POC) nucleic acid testing. Further, it may provide a handheld platform for miRNA single-nucleotide polymorphism analysis.

Paper-Based Optical Nose Made with Bimetallic Nanoparticles for Monitoring Ignitable Liquids in Gasoline

A paper-based optical nose was fabricated by dropping bimetallic silver and gold nanoparticles on a paper substrate. The nanoparticles were synthesized by both natural (lemon, pomegranate, and orange juices) and chemical (citrate, gallic acid, and ascorbic acid) reducing agents. The performance of the assay was evaluated for identifying gasoline and five ignitable liquids such as diesel, ethanol, methanol, kerosene, and thinner. The interaction of the sensor with sample vapors caused aggregation, consequently changing the color of nanoparticles. The color changes, which were captured by a scanner, represented a specified colorimetric map for each analyte, allowing one to identify the studied fuels. The visual results were confirmed using multivariate statistical analysis such as principal component analysis and hierarchical clustering analysis. Also, partial least-squares regression was used to assist the proposed assay for estimating the amount of studied ignitable liquids as counterfeit species in the gasoline sample. The root-mean-square errors for prediction were 3.4, 2.1, 1.9, 2.0, and 1.7% for diesel, thinner, kerosene, ethanol, and methanol, respectively. Finally, the fabricated sensor indicated high efficiency for the on-site detection of pure industrial gasoline samples from adulterated ones.

All-in-one: Accurate quantification, on-site detection, and bioimaging of sulfite using a colorimetric and ratiometric fluorescent probe in vitro and in vivo

SO₂ and its derivatives (SO₃^2-/HSO₃^-) are used widely in food, beverages, and pharmaceutical production. However, they could induce multiple diseases in respiratory, nervous, and cardiovascular systems. Although several fluorescent probes have been developed for detecting SO₃^2-/HSO₃^-, reports on rapid fluorescent probes for the on-site detection of SO₂ derivatives are scarce. Herein, a colorimetric and ratiometric fluorescent probe 1 based on the intramolecular charge transfer (ICT) was reported. Probe 1 resulted in a 122 nm blue-shift in fluorescent emission and decrement of absorbance at 500 nm upon the addition of sulfite. Therefore, probe 1 could quantify SO₃^2-/HSO₃^- using both UV-Vis and fluorescent methods (LOD: UV-Vis method 34 nM; fluorescent method 51 nM). Importantly, probe 1 was used for a rapid (60 s) and convenient (1 step, on-site) measurement of the SO₂ derivatives in real samples (LOD: 0.47 µM) using smartphone based on the colorimetric method. The SO₃^2-/HSO₃^--sensing mechanism was confirmed as the Michael addition reaction. Furthermore, the probe was used for the real-time monitoring of SO₃^2-/HSO₃^- in A549 cells and zebrafish. In summary, an all-in-one fluorescent probe was successfully developed for the accurate quantification, on-site detection, and bioimaging of SO₃^2-/HSO₃^-.

Lanthanide metal-organic framework as a paper strip sensor for visual detection of sulfonamide with smartphone-based point-of-care platform

Antibiotic residues in aquatic environments have attracted wide attention. Considering the impacts on the ecosystem and human health, it is urgent to develop a rapid method for detecting antibiotic residues in the environment. In this work, a nanoscale lanthanide metal-organic framework Eu(TATB) with a stable red luminescence in aqueous solution is synthesized by the microemulsion method. Sulfamethazine (SMZ) is frequently most used in veterinary medicine as one of sulfonamides. Eu(TATB) can be used for sensitively and rapidly specific recognition of SMZ with low detection limit (0.67 μM) and eminent recyclability. In addition, a paper-based visual system for point-of-care (POC) monitoring SMZ is devised by both using filter paper embedded with Eu(TATB) and our developed portable smartphone-involved imaging cassette. The naked eyes can observe that the red luminescence of the paper sensor gradually fades away at the presence of SMZ. This provides a reliable and effective method for on-site detection of sulfonamide antibiotics in the field of environmental monitoring.

Recent advances in synthesis and modification of carbon dots for optical sensing of pesticides

Serious threat from pesticide residues to the ecosystem and human health has become a global concern. Developing reliable methods for monitoring pesticides is a world-wide research hotspot. Carbon dots (CDs) with excellent photostability, low toxicity, and good biocompatibility have been regarded as the potential substitutes in fabricating various optical sensors for pesticide detection. Based on the relevant high-quality publications, this paper first summarizes the current state-of-the-art of the synthetic and modification approaches of CDs. Then, a comprehensive overview is given on the recent advances of CDs-based optical sensors for pesticides over the past five years, with a particular focus on photoluminescent, electrochemiluminescent and colorimetric sensors regarding the sensing mechanisms and design principles by integrating with various recognition elements including antibodies, aptamers, enzymes, molecularly imprinted polymers, and some nanoparticles. Novel functions and extended applications of CDs as signal indicators, catalyst, co-reactants, and electrode surface modifiers, in constructing optical sensors are specially highlighted. Beyond an assessment of the performances of the real-world application of these proposed optical sensors, the existing inadequacies and current challenges, as well as future perspectives for pesticide monitoring are discussed in detail. It is hoped to provide powerful insights for the development of novel CDs-based sensing strategies with their wide application in different fields for pesticide supervision.

Recent Advances and Applications in Paper-Based Devices for Point-of-Care Testing

Point-of-care testing (POCT), as a portable and user-friendly technology, can obtain accurate test results immediately at the sampling point. Nowadays, microfluidic paper-based analysis devices (μPads) have attracted the eye of the public and accelerated the development of POCT. A variety of detection methods are combined with μPads to realize precise, rapid and sensitive POCT. This article mainly introduced the development of electrochemistry and optical detection methods on μPads for POCT and their applications on disease analysis, environmental monitoring and food control in the past 5 years. Finally, the challenges and future development prospects of μPads for POCT were discussed.

Development and critical evaluation of a novel fluorescent nanosensor based on a molecularly imprinted polymer for the rapid detection of procymidone in ginseng

Effective methods are required to quantify the organochlorine pesticide procymidone due to its potentially harmful effects toward human health and the environment.

An α-naphtholphthalein-derived colorimetric fluorescent chemoprobe for the portable and visualized monitoring of Hg2+ by the hydrolysis mechanism

An ɑ-naphtholphthalein-derived colorimetric fluorescent chemoprobe was elaborately designed for the portable and visual monitoring of Hg2+ in environmental and biological samples.

A highly selective and sensitive CdS fluorescent quantum dot for the simultaneous detection of multiple pesticides

We presented one-pot prepared CdS fluorescent quantum dots (QDs) which can sensitively and selectively detect three different organic pesticides.

Enzyme-triggered click chemistry combined with surface-enhanced Raman spectroscopy for the simple and sensitive detection of alkaline phosphatase activity from complex biological samples

Schematic of the enzyme-triggered click chemistry combined with the SERS technique for ALP detection.

Chromaticity Evolutionary Detection of Food Contaminant Semicarbazide through an Upconversion Luminescence-Based Nanosensor

Semicarbazide (SEM) is a widespread carcinogenic and neurotoxic food contaminant, originating from the metabolite of antibiotic nitrofurazone, which is used in aquaculture, or thermal decomposition byproduct of a flour blowing agent azodicarbonamide. Although optical detection technologies are powerful tools considering the advantages of fast response and visualization detection, there are few optical nanosensors for highly sensitive and visual assays of SEM due to no luminescence response and UV absorbance of SEM. Herein, an upconversion luminescence (UCL)-based nanosensor was designed for visual detection of SEM with high sensitivity and good selectivity. The nanosensor was constructed by combining upconversion nanoparticles (UCNPs) and phosphomolybdic acid (PMA), which was used as the specific recognition element of SEM. The developed nanosensor exhibited selective absorbance enhancement and UCL quenching behavior with the addition of SEM based on the inner filter effect (IFE). Since the change in absorbance translated into an exponential change in the luminescence, the sensitivity of the nanosensor was greatly improved. The nanosensor realized a highly sensitive and visual response to SEM in the linear range of 0.5-16 μM with a low limit of detection of 58 nM. Moreover, satisfactory recovery values ranging from 90 to 112% in spiked real samples indicated the practical applicability of the nanosensor. The nanosensor designed here provides a sensitive and convenient sensing strategy for visual detection of hazardous substances and is expected to develop the upconversion sensing application in food safety.

A dual-signal fluorometric-colorimetric sensing platform and visual detection with a smartphone for the determination of β-galactosidase activity based on fluorescence silicon nanoparticles

As one of primary biomarkers of ovarian cancer in early stages, β-galactosidase (β-Gal) is significant in the discovery and diagnosis of the disease. In this work, we constructed a multi-signal sensing platform based on silicon nanoparticles (Si NPs) for β-Gal activity determination. When β-Gal was introduced to the sensing system, 2-Nitrophenyl β-D-galactopyranoside (ONPG) could be converted to o-Nitrophenol (o-NP), which had a characteristic absorption peak at 416 nm and the colorless solution turned yellow. The fluorescence emission of Si NPs at 450 nm can be greatly quenched by o-NP as a consequence of inner filter effect (IFE). This dual-signal fluorometric and colorimetric determination approach could be utilized to detect β-Gal in the range of 2-120 U/L and 6-120 U/L. The limits of detection were 1.36 U/L and 1.07 U/L, respectively. This sensing platform could be successfully utilized to detect β-Gal in real samples. Additionally, a visual detection method was designed to achieve quantitative analysis of β-Gal with the assistance of the smartphone.

A colorimetric and SERS dual-readout sensor for sensitive detection of tyrosinase activity based on 4-mercaptophenyl boronic acid modified AuNPs

Tyrosinase (TYR) is as a well-known polyphenol oxidase and important biomarker of melanocytic lesions. Thus, developing powerful methods to determine TYR activity is of great value in the early diagnosis of skin disease. Direct surface-enhanced Raman scattering (SERS) detection of biomolecules is usually affected by non-specific interference and complicate structure of the analytes. It is a challenge to develop Raman-active molecules with specific recognition to analytes in complex media. Here, we report a novel colorimetric and surface-enhanced Raman scattering (SERS) dual-readout assay for the determination of TYR using commercially available and economical 4-mercaptophenyl boronic acid (4-MPBA) as a Raman-active and recognition molecule. 4-MPBA provides a unique interactive boronic acid group to the diol group of TYR substrate and exhibits good SERS signal. Also, the introduction of magnetic beads could promptly improve the anti-interference ability of dual-mode sensor. The TYR-incubated tyramine-modified magnetic beads could obviously change the concentration of 4-MPBA-AuNPs in the presence of O₂ and ascorbic acid, where the ultraviolet visible (UV-vis) absorption and SERS intensity were directly related to the concentration of TYR added. The dual-mode sensor had a rapid response to TYR within 1 min under optimized conditions and had high selectivity for TYR with a limit of detection at 0.001 U/mL. In addition, the dual-mode strategy showed promising prospects in the determination of TYR activity in serum samples and could be used to screen TYR inhibitors.

Smartphone-assisted ratiometric fluorescence sensing platform and logical device based on polydopamine nanoparticles and carbonized polymer dots for visual and point-of-care testing of glutathione

As a crucial biothiol, glutathione (GSH) plays a key role in the organisms. Monitoring GSH level is of great significance for disease diagnosis and biomedical research. In this work, polydopamine (PDA) nanoparticles-red fluorescent carbonized polymer dots (r-CPDs) based ratiometric fluorescence sensing platform was constructed and employed for GSH assay. Dopamine (DA) could be oxidized by cobalt oxyhydroxide (CoOOH) nanosheets and further polymerized into PDA nanoparticles with green fluorescence. However, in the presence of GSH, CoOOH nanosheets were reduced and decomposed, which prevented the production of PDA nanoparticles. In the sensing system, green-emitting PDA nanoparticles were employed as a response unit and r-CPDs were used as an internal reference unit. With the addition of GSH, the green fluorescence of PDA nanoparticles decreased as well as the red fluorescence of system remained relatively stable. Importantly, a distinct fluorescence color evolution from green to red was presented with a serious of GSH concentrations. Based on this, a portable smartphone-assisted ratiometric chromaticity analytical method was developed to achieve the on-site visual detection of GSH. Both the established ratiometric fluorescence and ratiometric chromaticity sensing methods for GSH assay have the merits of wide linear range, high sensitivity and excellent accuracy, which are suitable for the determination of GSH in human serum and exhibit great application potential in rapid and accurate monitoring of the GSH levels in clinical. Moreover, an ingenious logical device reflecting GSH levels was designed based on the two different fluorescence signals, which provided a new strategy for the intelligent online detection of GSH in complex biological matrices.

Programmable-Printing Paper-Based Device with a MoS2 NP and Gmp/Eu-Cit Fluorescence Couple for Ratiometric Tetracycline Analysis in Various Natural Samples

Paper-based fluorescence devices, with smartphone aids, bring considerable operation convenience for tetracycline (TC) sensing. Nevertheless, they must meet the challenge in real determination against complicated backgrounds. Considering that, we present a programmable-printing paper-based device and then apply it to TC determination for various natural samples. MoS₂ NPs and Gmp/Eu-Cit are synthetized as composite probes. A static quenching process is found with MoS₂ NP fluorescence at 430 nm, while significant magnification of Gmp/Eu-Cit emission is obtained at 617 nm, establishing a valuable ratiometric indicator. Remarkably, two-stage programmable printing maximizes the proposed sensing capability. A transitive device, containing a gradually changing amount of a certain probe, is prepared to sense TC. With a homemade smartphone application and 3D-printed measurement chamber, the corresponding signals are examined to explore optimal setups. These setups are automatically processed to prepare the final-version device, not requiring manual operations. Benefitting from this interesting feature, the proposed device gains many rewards in performances. It effectively senses TC in a wide range from 12.7 nM to 80 μM and simultaneously provides naked eye-legible signals and smartphone-based readouts with confident selectivity and stability. This device is consequently applied for various samples of soil, river water, milk, and serum and meets well with HPLC-MS and recovery tests.

A Lab-in-a-Syringe Device Integrated with a Smartphone Platform: Colorimetric and Fluorescent Dual-Mode Signals for On-Site Detection of Organophosphorus Pesticides

Herein, a portable lab-in-a-syringe device integrated with a smartphone sensing platform was designed for rapid, visual quantitative determination of organophosphorus pesticides (OPs) via colorimetric and fluorescent signals. The device was chiefly made up of a conjugate pad labeled with cetyltrimethylammonium bromide-coated gold nanoparticles (CTAB-Au NPs) and a sensing pad modified by ratiometric probes (red-emission quantum dots@SiO₂ nanoparticles@green-emission quantum dots, rQDs@SiO₂@gQDs probe), which was assembled through a disposable syringe and reusable plastic filter. In the detection system, thiocholine (Tch), the hydrolysis product of thioacetylcholine (ATch) by acetylcholinesterase (AchE), could trigger the aggregation of CTAB-Au NPs, resulting in a significant color change from red to purple. Then, CTAB-Au NPs flowed vertically upward and bound to the rQDs@SiO₂@gQDs probe on the sensing pad, reducing the fluorescence resonance energy transfer effect between CTAB-Au NPs and gQDs. Meanwhile, rQDs embedded in SiO₂ NPs remained stable as internal reference fluorescence, achieving a color transition from red to green. Thus, based on the inhibition of AChE activity by OPs, a colorimetric and fluorescent dual-mode platform was constructed for on-site detection of OPs. Using glyphosate as a model, with the support of a color recognizer application (APP) on a smartphone, the ratio of red and green channel values could be utilized for accurate OP quantitative analysis ranging from 0 to 10 μM with a detection limit of 2.81 nM (recoveries, 90.8-122.4%; CV, 1.2-3.4%). Overall, the portable lab-in-a-syringe device based on a smartphone sensing platform integrated sample monitoring and result analysis in the field, implying great potential for on-site detection of OPs.