Colorimetric Dual-readout Assay Research Articles

Fluorometric and colorimetric quantitative analysis platform for acid phosphatase by cerium ions-directed AIE and oxidase-like activity.

A facile and sensitive fluorescent and colorimetric dual-readout assay for detection of acid phosphatase (ACP) was developed via Ce(III) ions-directed aggregation-induced emission (AIE) of glutathione-protected gold nanoclusters (GSH-AuNCs) and oxidase-mimicking activity of Ce(IV) ions. Free Ce(IV) ions exhibited a strong oxidase-mimetic activity, catalytically oxidizing colorless 3,3',5,5'-tetramethylbenzidine (TMB) into its blue product oxTMB in the presence of dissolved O2, thus triggering a remarkable color reaction detectedvisually. ACP can hydrolyze L-ascorbic acid-2-phosphate (AAP) with the production of ascorbic acid (AA). The AA is able to reduce Ce(IV) ions to Ce(III) ions, thus quenching the oxidase-mimetic activity of Ce(IV) ions. Meanwhile, Ce(III) ions induce AIE of GSH-AuNCs, resulting in the enhancement of thefluorescence signal of GSH-AuNCs. Both the fluorescent and colorimetric dual-mode analysis platforms exhibit a sensitive response to ACP, providing detection limits as low as 0.101 U/L and 0.200 U/L, respectively. Besides, this fabricated dual-mode detection platform holds the potential for analysis of ACP in human serum samples and screening inhibitors for ACP. With good performance and practicability, this study shows promising application in the convenient and reliable determination of ACP activity.

A fluorescent and colorimetric sensor based on ionic liquids for the on-site monitoring trace gaseous SO2

SO2 could cause severe environmental pollution and health threat, so real-time and on-site monitoring of SO2 has attracted considerable attention. This work proposed a novel ionic liquid-based sensor, called trihexyl (tetradecyl) phosphonium fluorescein ionic liquid, which can accurately detect SO2 with its fluorescent and colorimetric dual-readout assay without seventeen gases interference (eg: NO, N2, CO2, O2, COS, HCl, CHCl3). GC-MS was also used to verify the validation of the detection method. First, this fluorescein-based IL sensor exhibited fluorescence green and colorimetric yellow signals. When the sensor was exposed to gaseous SO2, the green fluorescence quenched, and the colorimetric yellow color faded due to chemical bond interaction. Also, the proposed IL sensor exhibited good linearity in the SO2 concentration range of 5.0–95.0 ppm with a detection limit of 0.9 ppm (fluorescence) and 1.9 ppm (colorimetry), and recoveries of 97%∼103% with RSD less than 1.21%. Besides, the IL sensor could be easily assembled into a paper device by simple immersion, and the paper strip was exploited to realize a semiquantitative visual detection of SO2. These results indicated that the proposed fluorescence-colorimetric dual-signal chemosensor could be used as intelligent paper labels for real-time and on-site monitoring of SO2 in ambient air.

Enzyme-free ratiometric fluorescence and colorimetric dual read-out assay for glyphosate with ultrathin g-C3N4 nanosheets

Herein, a sensing platform for the rapid quantitative detection of glyphosate with high sensitivity and selectivity was constructed by enzyme-free ratiometric fluorescence and colorimetric dual read-out assay based on ultrathin g-C3N4 nanosheets (UCN NS).Fluorescent diaminophenylazine (DAP) with fluorescence was from the oxidation of o-phenylenediamine (OPD) in the presence of Cu2+. DAP could inspire a significant fluorescence quenching of nanosheets due to photo-induced electron transfer (PET), therefore exhibiting a ratiometric fluorescence response. In the presence of glyphosate, the strong chelation of Cu2+ by glyphosate inhibited the oxidation of OPD, which reduced the fluorescence intensity of DAP, while the fluorescence of the ultrathin nanosheets was restored. Moreover, the oxidation of OPD (colorless) to DAP (yellow) was a distinctly visible color change process, which provides well-suited conditions for colorimetric analysis. At the optimum experimental conditions, the detection concentration range of glyphosate was 0.001–0.48 μg/mL, and the limit of fluorometric detection was 0.49 ng/mL (S/N = 3). This assay was simple and easy to use for the detection of glyphosate in food safety and the environment with satisfactory results.

A reliable fluorescent and colorimetric dual-readout assay for Ag+ tracing

Silver ion pollution is a great threat to global environment and public healthcare today. Thus, quick, portable and sensitive assays for Ag+ tracing are highly needed. Herein, a reliable fluorescent and colorimetric dual-channel assay has been constructed for Ag+ detection by utilizing a terbium-based fluorescent nanomaterial (named as Tb-DPA) and a Pt/Pd nanoflower (Pt/Pd NF)-triggered reaction between N-ethyl-N-(3-sulfopropyl)-3-methylaniline sodium salt (TOPS) and 4-amino-antipyrine (4-AAP). Initially, in the sensing system containing 4-AAP, TOPS, Tb-DPA and Pt/Pd NF, TOPS and 4-AAP is catalyzed by Pt/Pd NF to produce a purple compound (called as PC1), which endows a broad UV absorption that can fully cover the emission band of Tb-DPA. Thus, the system exhibits a high UV absorption (originating from PC1) and a low fluorescence intensity (originating from Tb-DPA) which has been quenched by PC1 through a filtering effect. However, when the system meets Ag+, the oxidase-like activity of Pt/Pd NF will be inhibited, leading less amount of PC1. As a result, the system exhibits a decreased UV absorption and a recovered fluorescence intensity, both of which can be used for Ag+ detection, reporting low detection limits of 3.63 nM and 1.63 nM, respectively. Specially, results from the dual-channel assay can mutually validate each other, improving the detection reliability. Moreover, this dual-mode assay shows good capability toward Ag+ detection in real samples, illustrating the potential for practical applications.

Fluorometric and Colorimetric Dual-Readout Assay for Histone Demethylase Activity Based on Formaldehyde Inhibition of Ag+-Triggered Oxidation of O-Phenylenediamine.

Histone demethylases (HDMs) are vital players in epigenetic regulation and important targets in cancer treatment, but effective molecular tools for analyzing HDMs activity are still limited. Interestingly, we found that the process of Ag+-triggered oxidation of O-phenylenediamine (OPD) to 2,3-diaminophenazine (OPDox) could be efficiently inhibited by formaldehyde (HCHO), with the decrease of fluorescent and colorimetric signals from OPDox. Accordingly, we developed a novel label-free fluorescent and colorimetric dual-readout assay for HDMs activity based on direct quantitation of HCHO liberated in the demethylation process. On the basis of the excellent performance of the Ag+-OPD-based method for HCHO quantitation, lysine-specific demethylase 1(LSD1) activity was not only successfully detected with a low detection limit of 0.3 nM (fluorescence) and 0.5 nM (colorimetric) but also observed by the naked eye. Moreover, the feasibility of the proposed assay was further expanded to assess the LSD1 activity in cancer cell lysate and its inhibition through a mix-and-readout procedure. This label-free, cost-effective, and highly sensitive dual-readout assay presents a valuable tool for epigenetics research and drug discovery.

Fluorometric and colorimetric determination of hypochlorite using carbon nanodots doped with boron and nitrogen.

Carbon nanodots doped with boron and nitrogen (BN-CDs) with an average diameter of around 11nm were prepared by a hydrothermal approach using adenine and 3-aminobenzene boronic acid as the starting materials. The atomic ratio of boron to nitrogen atomic in the BN-CDs is approximately 1:1. This indicates that a large fraction of N atoms goes lost during preparation because the B/N ratio of the precursors is about 1:6. The BN-CDs display blue fluorescence (best measured at excitation/emission wavelengths of 305/380nm) which is independent of the excitation wavelength. On exposure to hypochlorite anion, fluorescence is quenched and the color of the solutions changes from yellow to brown. Fluorescence drops linearly in the 0.1-1000μM hypochlorite concentration range. The colorimetric response, best measured as the absorbance ratioat 236/260nm, ranges from 0.3 to 4.0mM. The color changes can be readily detected visually. The probe was applied to the determination of hypochlorite in living cells and in (spiked) tap water. Graphical abstract Excitationwavelength-independent fluorescent boron and nitrogen codoped carbon nanodots (BN-CDs) were obtainedbya hydrothermal approach. The BN-CDs were usedto detect hypochlorite in wastewaterby afluorometric and colorimetric dual-readout assay.

Molecular structure regulation and enzyme cascade signal amplification strategy for upconversion ratiometric luminescent and colorimetric alkaline phosphatase detection

Herein, molecular structure regulation and enzyme cascade signals amplification (MRECAmp) strategy was proposed to construct a novel upconversion ratiometric fluorescence and colorimetric dual-readout assay platform for highly sensitive and selective detection of alkaline phosphatase (ALP) activity. The detection strategy is divided into three aspects. Firstly, Ag+ oxidates o-phenylenediamine (OPD) to 2,3-diaminophennazine (OPDox), which can significantly quench upconversion fluorescence at 487 nm based on inner filter effects (IFE) while the upconversion emission at 668 nm was essentially unchanged for Zn2+-doped NaYF4:Yb3+,Er3+,Tm3+ upconversion nanoparticles (UCNPs) probes under the near-infrared (NIR) irradiation. Secondly, ALP catalyzes the hydrolysis of the substrate l-ascorbic acid 2-phosphate (AAP) to ascorbic acid (AA) which can consume part of Ag+ to inhibit the generation of OPDox and the AA was oxidized to dehydroascorbic acid (DHAA). The specific performance of DHAA molecular structure regulation, due to the condensation reaction between dicarbonyl group of DHAA and diamine group of OPD, that is confirmed by ESI-MS and 1H NMR spectra analysis, can remarkably enhance the selectivity of ALP detection, which is conceptually different from the previously reported ALP fluorescent assays. Thirdly, the generated DHAA reacts with OPD to form 3-(dihydroxyethyl)furo [3,4-b]quinoxaline-1-one (DFQ) that further inhibits the generation of OPDox, which makes the enzyme-controlled cascade signal amplification (ECAmp) can be realized with a great fluorescence recovery (60.04%) at 487 nm. Therefore, the fluorescence response signal ((I487/I668)0/(I487/I668)) is amplified by ECAmp strategy, allowing the quantitative analysis of ALP with a detection limit of 0.03 mU/mL. The detection of ALP activity in human serum samples over the conventional methods demonstrates that the MRECAmp method provides a sensing platform for probing ALP activity and shows promising outlook in biomedical studies.

Non-oxidation reduction strategy for highly selective detection of ascorbic acid with dual-ratio fluorescence and colorimetric signals

Ascorbic acid (AA), one of the most important vitamins, acts a critical role in various physiological reactions and is involved in many diseases. Thus, the development of highly selectivity methods for detecting AA level with the presence of different reducing substances is of great significance in complicated serum matrix. In this paper, a non-oxidation reduction regulation (NRR) strategy was designed to construct a novel dual-ratio fluorescence and colorimetric dual-readout assay for highly selective detection of AA. The strategy involves three processes: Ag+ oxidated o-phenylenediamine (OPD) to 2,3-diaminophenazine (OPDox), AA inhibited the generation of OPDox and the AA was oxidized to dehydroascorbic acid (DHAA). The specific performance of DHAA NRR, due to the condensation reaction between dicarbonyl group of DHAA and diamine group of OPD, that is confirmed by ESI-MS and 1H NMR spectra analysis, can remarkably enhance the selectivity of AA detection. Additionally, the proposed method based on NRR strategy not only provides a sensing platform for probing AA but also shows promising outlook in biomedical studies.

A cyclic signal amplification strategy to fluorescence and colorimetric dual-readout assay for the detection of H2O2-related analytes and application to colorimetric logic gate

We report a novel facile upconversion fluorescent and colorimetric dual-readout assay for H2O2 as well as H2O2-related analytes via enzyme-controlled cyclic signal amplification strategy. As a proof of application demonstration, the highly sensitive detection of choline and acetylcholine chloride (ACh) was performed. This sensing strategy involves the reaction of ACh with acetylcholinesterase (AChE) to generate choline which is followed catalytically oxidized by choline oxidase (ChOx) to produce H2O2. The generated H2O2 can transform Fe2+ to Fe3+ and free hydroxyl radical (OH). The as-produced Fe3+ and OH can simultaneously oxidize o-phenylenediamine (OPD) to 2,3-diaminophennazine (OPDox) and the Fe3+ was reduced to Fe2+. The Fe2+ produced from the redox processes between Fe3+ and OPD could be cycle used to generate OPDox that can significantly quench upconversion nanoparticles (UCNPs) fluorescence based on inner filter effects (IFE) and cause a visible change from colorless to yellow color. The phenomenon is further designed as a colorimetric logic gate. Moreover, we also detected H2O2, glucose, lactate and uric acid (UA) with the higher sensitivity by utilizing the assay strategy, which revealed the extensive applications of the proposed sensing strategy in biomedical analysis.

In Situ Fluorogenic and Chromogenic Reactions for the Sensitive Dual-Readout Assay of Tyrosinase Activity.

As a well-known copper-containing oxidase, tyrosinase has been anticipated to serve as the biomarker of skin diseases. We describe here an exquisite label-free fluorescent and colorimetric dual-readout assay of its activity, inspired by the specific oxidation ability of monophenolamine substrates to catecholamines and a unique fluorogenic reaction between resorcinol and catecholamines. By employing commercially available tyramine as the model substrate (dopamine as the product), it is found that the tyrosinase-incubated tyramine solution exhibits obvious pale yellow with intense blue fluorescence in the presence of resorcinol and O2, where the absorbance and fluorescence intensity are directly related to the concentration of added tyrosinase (i.e., the amount of conversion of tyramine to dopamine). The overall process of sensing tyrosinase activity takes less than 100 min at ambient temperature and pressure conditions with exceedingly simple operation procedure, explicit response mechanism, and formation of fluorophore with high quantum yield from scratch. Furthermore, such a convenient, rapid, cost-effective, and highly sensitive dual-readout assay exhibits promising prospect for the tyrosinase activity in extensive bioassays and clinic research as well as in screening potential tyrosinase inhibitors.

Fluorescence turn-on and colorimetric dual readout assay of glutathione over cysteine based on the fluorescence inner-filter effect of oxidized TMB on TMPyP

Quantitative fluorescence turn-on and colorimetric detection of glutathione (GSH) with rapid speed, low cost have attained much attention. Herein, we developed a sensitive fluorescence turn-on and colorimetric sensor for GSH based on the inner-filter effect (IFE), which is the first time to select oxTMB and TMPyP as the IFE absorber and fluorophore pair, respectively. The absorption band of oxTMB matches well with the emission band of TMPyP in the IFE-based fluorescent assay. In the absence of GSH, the absorption peak of oxTMB at 652nm significantly overlaps with the emission of TMPyP, resulting in the efficient IFE and inhibition of the fluorescence of TMPyP. In the presence of GSH, the absorption intensity at 652nm decreases, generating the recovery of the fluorescence of TMPyP. Therefore, this approach is demonstrated to be a novel candidate for detection of GSH, with high sensitivity and selectivity. The linear dynamic range for the concentrations of GSH is between 0.1μM to 20μM along with a limit of detection (LOD) of about 30nM (calculated LOD as 3σ/slope). Finally, this novel sensor was successfully applied for GSH detection in fetal calf serum, and satisfactory recovery was achieved.