An ratiometric fluorescence immunosensor Mn-triggered aggregation-induced emission transformation of levodopa fluorescent copolymer nanoparticles.

Herein, a direct alkaline phosphatase (ALP)-labeled luminescent nanoimmunoassay platform was constructed using Mn-triggered aggregation-induced emission transformation of levodopa fluorescent copolymer (LFC) nanoparticles. Using cardiac troponin I (cTn I) as the model antigen, the proposed nanoimmunosensor has been applied to detect cTn I in clinical samples with satisfactory results.

An alkaline phosphatase-induced immunosensor for SARS-CoV-2 N protein and cardiac troponin I based on the in situ fluorogenic self-assembly between N-heterocyclic boronic acids and alizarin red S.

Alkaline phosphatase (ALP)-induced in situ fluorescent immunosensor is less investigated and reported. Herein, a high-performance ALP-labeled in situ fluorescent immunoassay platform was constructed. The developed platform was based on a fluorogenic self-assembly reaction between pyridineboronic acid (PyB(OH)) and alizarin red S (ARS).

Simple construction of a two-component fluorescent sensor for turn-on detection of Hg in human serum.

The simply constructed fluorescent sensor with inexpensive reagents and low toxicity has attracted increasing attention contributing to its practical application. However, the common construction methods usually required a few building blocks and complex procedures, which is inconvenient for their further application. Herein, a simply constructed fluorescent Hg sensor has been developed based on the intrinsic fluorescence quenching power of G-quadruplex.

A colorimetric and ratiometric photometric sequential assay for ascorbic acid and alkaline phosphatase in serum based on valence states modulation.

The photometric method is widely used in real clinical tests due to its simple operation, low cost and convenient. Many of the reported colorimetric ALP assays so far are non- ratiometric because the detection was based on changes in absorbance at a single wavelength. The development of novel colorimetric and ratiometric assay is of importance for quantitatively measuring target with high accuracy.

An improved structure-switch aptamer-based fluorescent Pb biosensor utilizing the binding induced quenching of AMT to G-quadruplex.

An improved aptamer-based fluorescent Pb biosensor utilizing the binding induced quenching of AMT to G-quadruplex has been rationally designed with a LOD of 3.6 nM. The utility of the developed biosensor was demonstrated by the successful detection of Pb in real complex clinical samples with satisfactory recovery and good reproducibility.

Design of a Fluorescence Turn-on and Label-free Aptasensor Using the Intrinsic Quenching Power of G-Quadruplex to AMT.

A novel fluorescent aptasensor based on the G-quadruplex induced fluorescent quenching of psoralen and the competitive interactions between 4'-aminomethyl-4,5',8-trimethylpsoralen (AMT), adenosine triphosphate (ATP) and G-rich DNA functionalized split ATP aptamer was proposed. The binding of ATP to the G-rich DNA functionalized split aptamer induced a significant enhancement in fluorescence emission intensity while undergoing excitation at 340 nm. Under the optimal conditions, the developed aptasensor showed high selectivity and good accuracy for detecting ATP.

Design of a nanoswitch for sequentially multi-species assay based on competitive interaction between DNA-templated fluorescent copper nanoparticles, Cr and pyrophosphate and ALP.

The present work constructs a sequentially triggered nanoswitch (STN) for sequential detection of Cr, PO (PPi) and alkaline phosphatase (ALP) depending on polythymine (T40) templated fluorescent Cu nanoparticles (Cu NPs). A significant phenomenon is that Cr can only causing 5% QE of fluorescent Cu NPs synthesized by lower than 500 μM Cu, but the fluorescence of the Cu NPs synthesized by more than 500 μM Cu can be quenched up to 90% QE by the same concentration of Cr. Then the quenched fluorescence of CuNP-Cr complex provides a sensing platform for PPi due to the strong binding between Cr and PPi, resulting in dissociation of Cr from the surface of Cu NPs and the recovery of fluorescence emission.

Development of luminescent nanoswitch for sensing of alkaline phosphatase in human serum based onAl3+-PPi interaction and Cu NCs with AIE properties.

As an important biomarker, alkaline phosphatase (ALP) is one of the most commonly assayed enzymes in clinical practice. Here a novel turn-on fluorescent nanoswitch for ALP assay was suggested. The nanoswitch was easily constructed via two high-affinity ligands between GSH and Al and PPi and Al based on the difference in the affinity.

Novel strategy to improve the sensing performances of split ATP aptamer based fluorescent indicator displacement assay through enhanced molecular recognition.

Split aptamer strategy was often used to improve the sensitivity of aptasensor. However, traditional split aptamer strategy can not be directly used to improve the label-free aptamer based Thioflavin T (ThT) displacement assay for ATP because the split ATP aptamer display much lower enhancement effects on the fluorescence of ThT than intact aptamer. In order to address this issue, this is the first report using G-rich DNA sequence to enhance the affinity of the two split ATP aptamer halves to ThT and offer lower limit of detection (LOD), wider linear range and higher selectivity through the enhanced molecular recognition.

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.

A label-free fluorescent molecular switch for a DNA hybridization assay utilizing a G-quadruplex-selective auramine O.

A sensitive and selective assay of DNA is developed by utilizing a signal transduction strategy with the rational redesign of the hairpin structured G-quadruplex molecular switch (G4-MS) assembled using auramine O (AO). By monitoring the changes of the fluorescent signal, we could identify and further quantitatively determine the target DNA in the samples.

A label-free oligonucleotide based thioflavin-T fluorescent switch for Ag+ detection with low background emission.

A novel fluorescent Ag(+) sensor was developed based on the label-free silver (I) specific oligonucleotide (SSO) and Thioflavine T (ThT) monomer-excimer switch. C-rich SSO which contain C-C mismatched base pairs can selectively bind to Ag(+) ions and the formed duplexes which constructed by C-Ag(+)-C structure are thermally stabilized without largely altering the double helical structure. ThT give very weak fluorescent in bulk solution and/or in the presence of SSO.

Design of a dual-signaling sensing system for fluorescent ratiometric detection of Al3+ ion based on the inner-filter effect.

A dual-signal sensing system based on the inner-filter effect (IFE) was demonstrated, in which the combination of two signaling mechanisms allows metal binding to turn on two fluorescence emission bands, independently. A proof-of-concept fluorescent ratiometric assay for Al(3+) in pure aqueous solution is presented. The proposed assay is based on the Al(3+)-induced color and fluorescence changes of Alizarin red S (ARS) and IFE between ARS and meso-tetra(N-methyl-4-pyridyl)porphine tetratosylate salt (TMPyP).

Oligonucleotide-based label-free Hg2+ assay with a monomer-excimer fluorescence switch.

A novel fluorescent Hg(2+) sensor was developed based on the T-Hg(2+)-T structure and a thioflavine T monomer-excimer fluorescent switch. Under optimum conditions, the selectivity is remarkably high, and Hg(2+) can be quantified over the dynamic range of 0.1 to 1.