Stimuli-responsive aggregation-induced emission of molecular probes by electrostatic and hydrophobic interactions: Effect of organic solvent content and application for probing of alkaline phosphatase activity

Construction of an end-repairing-engineered quadratic in vitro transcription machine for single-molecule monitoring of alkaline phosphatase in human cancers

Alkaline phosphatase (ALP) is an essential hydrolase widely present in humans, and it extensively acts as a biomarker for multiple human diseases. Conventional ALP assays suffer from complicated synthesis, tedious operation, low sensitivity, and large sample consumption. Herein, we construct an end-repairing-engineered quadratic in vitro transcription machine for single-molecule monitoring of ALP in diverse cancers with 3'-phosphoryl (PO4) nucleic acid as a macromolecular substrate. In presence of ALP, it catalyzes the removal of 3'-PO4 group to yield a 3'-hydroxyl end in hairpin probe 1 (HP1). Under the catalysis of Taq ligase, 3'-hydroxylated HP1 and hairpin probe 2 (HP2) are ligated together to form an intact transcription template. With the addition of T7 RNA polymerase, in vitro transcription amplification is activated to synthesize numerous reporter probes. Resulting reporter probes can bind with signal probes to initiate duplex-specific nuclease (DSN)-aided cyclic degradation of signal probes. Eventually, multiple cycles of degradation-liberation-hybridization induce the generation of large amounts of FAM fluorophores that are counted via single-molecule imaging. Due to high specificity of ALP-directed 3'-end dephosphorylation, high efficiency of quadratic in vitro transcription cascades, and ultrahigh signal-to-noise ratio (SNR) of single-molecule counting, this machine can detect ALP with a limit of detection (LOD) of 7.93 × 10-8 U/μL in vitro and 1 cell in vivo. Furthermore, it can be applied for the evaluation of enzyme kinetics, screening of potential antidrugs, and quantification of ALP level in various cancer cells and human serums, holding potential in 3'-phosphatases-associated biological study and clinical diagnosis.

Nanolabels Prepared by the Entrapment or Self-Assembly of Signaling Molecules for Colorimetric and Fluorescent Immunoassays

Nanomaterials have attracted significant attention as signal reporters for immunoassays. They can directly generate detectable signals or release a large number of signaling elements for readout. Among various nanolabels, nanomaterials composed of multiple signaling molecules have shown great potential in immunoassays. Generally, signaling molecules can be entrapped in nanocontainers or self-assemble into nanostructures for signal amplification. In this review, we summarize the advances of signaling molecules-entrapped or assembled nanomaterials for colorimetric and fluorescence immunoassays. The nanocontainers cover liposomes, polymers, mesoporous silica, metal-organic frameworks (MOFs), various nanosheets, nanoflowers or nanocages, etc. Signaling molecules mainly refer to visible and/or fluorescent organic dyes. The design and application of immunoassays are emphasized from the perspective of nanocontainers, analytes, and analytical performances. In addition, the future challenges and research trends for the preparation of signaling molecules-entrapped or assembled nanolabels are briefly discussed.

Synthesis of tetraphenylethylene-based small molecular sensor for the selective "turn-on" detection of pyrophosphoric acid in the aqueous solution

Pyrophosphoric acid (PPi) is a crucial indicator for monitoring adenosine triphosphate hydrolysis processes, and abnormal PPi levels in the human body seriously threaten human health. Thus the efficient detection of the concentration of PPi in the aqueous solution is important and urgent. This paper described the successful synthesis of a tetraphenylethylene (TPE) derivative, named as TPE-4B, which contained four chelate pyridinium groups exhibiting aggregation-induced emission characteristics. TPE-4B was explicitly developed for the selective and sensitive fluorescence detection of PPi in aqueous solutions, showing a fluorescence "turn-on" response, and the detection limit was 65 nM. The four chelate pyridinium moieties of TPE-4B exhibited robust electrostatic interactions and binding capacity towards PPi, leading to the formation of aggregations, which was confirmed by zeta potential, dynamic light scattering, and scanning electron microscopy. Compared with free TPE-4B in the aqueous solution, the zeta potential of aggregations decreased from 20.7 to 4.2 mV, the average diameter increased from 155 to 403 nm, and the morphology transformed from porous nanostructures into a block-like format. Leveraging these properties, TPE-4B is a promising candidate for a "turn-on" fluorescence sensor designed to detect PPi in the aqueous solution.