Cytoplasmic Protein-Powered In Situ Fluorescence Amplification for Intracellular Assay of Low-Abundance Analyte

Fibroblast activation protein-sensitive polymeric nanobeacon for early diagnosis of renal fibrosis

Early diagnosis and treatment of renal fibrosis (RF) significantly affect the clinical outcomes of chronic kidney diseases (CKDs). As the typical fibrotic ailment, RF is characterized by remodeling of the extracellular matrix, and the activation of fibroblast activation protein (FAP) plays a crucial role in the mediation of extracellular matrix protein degradation. Therefore, FAP can serve as a biomarker for RF. However, up to now, no effective tools have been reported to diagnose early-stage RF via detecting FAP. In this work, a polymeric nanobeacon integrating an FAP-sensitive amphiphilic polymer and fluorophores was proposed, which was used to diagnose early RF by sensing FAP. The FAP can be detected in the range of 0 to 200 ng/mL with a detection limit of 0.132 ng/mL. Furthermore, the fluorescence imaging results demonstrate that the polymeric nanobeacon can sensitively image fibrotic kidneys in mice with unilateral ureteral occlusion (UUO), suggesting its potential for early RF diagnosis and guidance of FAP-targeted treatments. Importantly, when employed alongside with non-invasive diagnostic techniques like magnetic resonance imaging (MRI) and serological tests, this nanobeacon exhibits excellent biocompatibility, low biological toxicity, and sustained imaging capabilities, making it a suitable fluorescent tool for diagnosing various FAP-related fibrotic conditions. To our knowledge, this study represents the first attempt to image RF in early stage by detecting FAP, offering a promising fluorescent molecular tool for diagnosing various FAP-associated diseases in the future.

Core-shell "loading-type" nanomaterials enabling glucometer readout for portable and sensitive detection of p-aminophenol in real samples

A one-target-many-trigger signal model sensing strategy is proposed for quickly, sensitive and on-site detection of the environmental pollutant p-aminophenol (PAP) by use of a commercial personal glucose meter (PGM) for signal readout with the core-shell "loading-type" nanomaterial MSNs@MnO2 as amplifiable nanoprobes. In this design, the mesoporous silica nanoparticles (MSNs) nanocontainer with entrapped signal molecule glucose is coated with redoxable manganese dioxide (MnO2) nanosheets to form the amplifiable nanoprobes (Glu-MSNs@MnO2). When encountered with PAP, the redox reaction between the MnO2 and PAP can induce the degradation of the outer layer of MSNs@MnO2, liberating multiple copies of the loaded glucose to light up the PGM signal. Owing to the high loading capability of nanocarriers, a "one-to-many" relationship exists between the target and the signal molecule glucose, which can generate adequate signal outputs to achieve the requirement of on-site determination of environmental pollutants. Taking advantage of this amplification mode, the developed PAP assay owns a dynamic linear range of 10.0-400 μM with a detection limit of 2.78 μM and provides good practical application performance with above 96.7 ± 4.83% recovery in environmental water and soil samples. Therefore, the PGM-based amplifiable sensor for PAP proposed can accommodate these requirements of environment monitoring and has promising potential for evaluating pollutants in real environmental samples.

A Polymeric Nanobeacon for Monitoring the Fluctuation of Hydrogen Polysulfides during Fertilization and Embryonic Development

Fertilization and early embryonic development as the beginning of a new life are key biological events. Hydrogen polysulfide (H₂ S_n ) plays important roles during physiological regulation, such as antioxidation-protection. However, no report has studied in situ H₂ S_n fluctuation during early embryonic development because of the low abundance of H₂ S_n and inadequate sensitivity of probes. We herein construct a polymeric nanobeacon from a H₂ S_n -responsive polymer and fluorophores, which is capable of detecting H₂ S_n selectively and of signal amplification. Taking the zebrafish as a model, the polymeric nanobeacon revealed that the H₂ S_n level was significantly elevated after fertilization due to the activation of cell multiplication, suppressed partially during embryonic development, and finally kept steady up to zebrafish emergence. This strategy is generally accessible for biomarkers by altering the responsive unit and significant for facilitating biological analysis during life development.

Self-Immolative Dye-Doped Polymeric Probe for Precisely Imaging Hydroxyl Radicals by Avoiding Leakage

For sensing low abundance of biomarkers, utilizing nanocarriers to load dyes is an efficient method to amplify the detected signal. However, the non-specific leak of the internal dyes in this approach is accompanied by false positive signals, resulting in inaccurate signal acquirement. To address this issue, in this work, we reported a novel signal amplification strategy with dye as a scaffold to construct a self-immolative dye-doped polymeric probe (SDPP). In our proposed approach, the dyes were covalently integrated into the main chain of a polymer, which can avoid the non-specific leak of the dye when used in a rigorous biological environment, thus evading the false positive signal. As a prototype of this concept, a SDPP, which responds to hydroxyl radicals (^•OH), was rationally fabricated. Upon being activated by ^•OH, SDPP will liberate the dye through a self-immolative reaction to bind with protein for amplifying the fluorescence signal. Compared with a dye-loaded nanoprobe, SDPP can precisely track intracellular basal ^•OH levels and visualize the ^•OH associated with myocarditis in vivo. More importantly, the attempt in this work not only provides an effective molecular tool to investigate the role of ^•OH in cardiopathy, but also puts forward a new direction to current signal-amplifying strategies for precisely and reliably acquiring the intracellular molecular information.

Noncovalently Caged Firefly Luciferins Enable Amplifiable Bioluminescence Sensing of Hyaluronidase-1 Activity in Vivo

Hyaluronidase 1 (Hyal-1) is an important enzyme involved in intracellular hyaluronic acid (HA) catabolism for performing various physiological functions, and its aberrant level is closely associated with many malignant diseases. Bioluminescence imaging is advantageous for monitoring Hyal-1 activity in vivo, but it remains challenging to design an available probe for differentiating Hyal-1 from other isoforms by a traditional strategy that covalently masks the firefly luciferase substrate. Herein, we, for the first time, present a noncovalently caging approach to construct a Hyal-1-specific bioluminogenic nanosensor by entrapping d-luciferin (d-Luc) inside the cholesterylamine-modified HA (CHA) nanoassembly to inhibit the bioluminescence production. When encountered with intracellular Hyal-1, CHA could be fully dissembled to liberate multiple copies of the loaded d-Luc, thereby emitting light by the luciferase-catalyzed bioluminescence reaction. Because of its cascade signal amplification feature, d-Luc@CHA displayed a remarkable "turn-on" response (248-fold) to 5 μg/mL Hyal-1 with a detection limit of 0.07 ng/mL. Importantly, bioluminescence imaging results validated that d-Luc@CHA could be competent for dynamically visualizing endogenous Hyal-1 changes in living cells and animals and possessed the capability of discriminating between normal and cancer cells, thus offering a promising toolbox to evaluate Hyal-1 roles in biological processes as well as to diagnose Hyal-1-related diseases.

In Vivo Imaging of Hypoxia Associated with Inflammatory Bowel Disease by a Cytoplasmic Protein-Powered Fluorescence Cascade Amplifier

Accurate and sensitive imaging of hypoxia associated with inflammatory bowel disease (IBD) is significant for the precise diagnosis and treatment of this disease, but it remains a challenge for traditional hypoxia-activatable fluorescence probes because of a more moderate hypoxic state during IBD than under other pathological conditions. To address this issue, herein, we designed a hypoxia-activatable and cytoplasmic protein-powered fluorescence cascade amplifier, named HCFA, to image hypoxia associated with IBD in vivo. In our design, a 4-aminobenzoic acid (azo)-modified mesoporous silica nanoparticle (MSN) was used as a container to load black hole quencher 2 (BHQ2) and cytoplasmic protein-binding squarylium dye (SQ); then, the β-cyclodextrin polymer (β-CDP) combined with azo through a host-guest interaction to form HCFA. Upon passive stagnation in the inflamed tissue of IBD, the azo band would be cleaved under a hypoxic microenvironment, and SQ was released to activate the fluorescence of HCFA. Moreover, the unconstrained SQ can bind with cytoplasmic protein to exhibit drastic fluorescence intensity enhancement, realizing the fluorescence signal amplification for imaging of hypoxia. When one takes advantage of the large load capacity of MSN and the unique property of SQ, HCFA can sense oxygen levels in the range of 0% to 10%. Meanwhile, the fluorescence imaging results demonstrate that HCFA can sensitively distinguish different levels of cellular hypoxia and monitor the variations of hypoxia in vivo, highlighting HCFA as a promising tool for the detection of hypoxia associated with IBD.