General Strategy to Achieve Color-Tunable Ratiometric Two-Photon Integrated Single Semiconducting Polymer Dot for Imaging Hypochlorous Acid

Triple-Standard Hypochlorite Quantitative Array Enabled by Precise Stokes Shift Modulation in D-π-A Chemodosimeters

The rational design of the D-π-A chemodosimeter with a significant Stokes shift is of great importance for enhancing the visualization of optical sensing signals. Here, three D-π-A fluorescent chemodosimeters with 2-(3-cyano-4,5,5-trimethylfuran-2(5H)-ylidene) malononitrile (TCF) as the electron-withdrawing group are synthesized by precisely modulating the electron-releasing strength. By decreasing the ability of electron release, the electrophilicity of the recognition site is increased by 1.449 kcal/mol, the Stokes shift of the chemodosimeter is improved to 201 nm, and the sensing mode changes from fluorescence quenching to ratiometric fluorescence and finally to fluorescence on. Furthermore, the three D-π-A fluorescent chemodosimeters display superior sensing performance toward ClO-, including low limits of detection (LOD, 37.0, 5.1, and 1.0 nM), rapid response (<5 s), and great selectivity in the presence of 16 kinds of interferents. Moreover, the practicality of the chemodosimeters is further validated by a portable triple-standard quantitative array detection platform, which can quantitatively detect ClO- solutions. The proposed design and modulation strategy for chemodosimeters can provide a new pathway for the sensitive and visualized identification of oxidants and other hazardous chemicals.

Organic Molecules as a Bridge Connecting Photoelectrochemistry and Fluorescence for Dual-Signal Assay

We report a strategy based on pyridyl-anchored organic small-molecule fluorescent probes to develop a dual-signal sensing platform. The strategy accomplishes an intelligent integration of fluorescence analysis with photoelectrochemical (PEC) sensing, thereby enabling rapid and precise detection of hypochlorite. In this work, the natural dye chromone was selected as the fluorophore for generating fluorescent signals. Meanwhile, by using phenothiazine (PTZ) as the specific recognition group and pyridine as the anchoring moiety, we designed and synthesized a novel organic small-molecule fluorescent probe. The obtained probe was used as a photosensitive material anchored to the TiO2 surface via N → Ti bonds, to form an FTO/TiO2/FPTZ-1 heterostructure-based dual-signal sensing platform for the detection of hypochlorite. This sensing platform has the characteristics of high specificity, sensitivity, and ease of preparation, enabling rapid qualitative fluorescence readout and quantitative photoelectrochemical readout of hypochlorite, with a limit of detection of 0.288 μM for fluorescence and 1.37 nM for PEC.

Rational design of hypochlorous acid-activatable fluorescent probe for diagnostic imaging and therapeutic evaluation in breast cancer recurrence

The recurrent breast cancer (BC) has elicited significant concern due to its rising recurrence rates and associated mortality. However, there is currently no effective detection method to mitigate the deterioration of BC recurrence. The imbalance of HClO content could lead to oxidative stress in the body, which damaging host tissues. Additional, improper regulation of HClO may exacerbate the progression of BC and promote the metastasis of BC cells. Accurately diagnosing and monitoring the HClO levels is crucial for treating BC recurrence. Traditional fluorescent probes for HClO exhibit several limitations, including poor selectivity, susceptibility to photobleaching, a small Stokes shift, and vulnerability to disturbances from excitation and fluorescence self-absorption, which undermine the precise detection of target analytes and restrict their biological applications. Herein, rational designed hypochlorous acid-activatable fluorescent probe (QPIO) was synthesized based on phenothiazine (PZ), quinoline malononitrile (QM), and hemicyanine, which demonstrated high anti-interference capability and a significant Stokes shift for HClO detection. Under various stimuli, QPIO was able to monitor HClO levels in RAW 264.7 and 4T1 cells in the red channel. Furthermore, it elucidated the correlation between HClO concentration and the progression of BC recurrence. Consequently, QPIO was utilized to diagnose recurrent BC, track therapeutic progress, and monitor the recurrence status of breast tumors in mouse models through in vivo HClO fluorescence imaging. It was demonstrated that a close relationship exists between the dynamic changes in HClO levels and BC recurrence, potentially advancing the understanding of the early diagnosis and development of therapeutic agents for recurrent BC.

Engineering Acid-Promoted Two-Photon Ratiometric Nanoprobes for Evaluating HClO in Lysosomes and Inflammatory Bowel Disease

HClO is considered a potential contributing factor and biomarker of inflammatory bowel disease (IBD). Accurate monitoring of lysosomal HClO is important for further developing specific diagnostic and therapeutic schedules for IBD. However, only rare types of fluorescent probes have been reported for detecting HClO in IBD so far. Herein, an acid-promoted two-photon semiconducting polymer dot (Lyso-RS Pdot) with dual emission in green and red channels and dual-sensing sites is successfully fabricated with two newly designed polymers NADE-PSMA and PFNA-10TBT as precursors. The red conjugated polymer PFNA-10TBT with pH-inert and HClO-sensitive units is employed to evaluate the HClO concentration in turn-off fluorescence. Meanwhile, the amphiphilic green fluorescent polymer NADE-PSMA sensitive to pH and HClO is employed to evaluate the pH value or HClO concentration in turn-on fluorescence. The resultant Lyso-RS Pdots not only display satisfactory performances for detecting HClO and pH but also achieve accurate two-photon imaging of HClO in lysosomes and the colon of IBD mice based on the distinguished properties such as ratiometric signal output, acid-promoted signal amplification, ultrafast response, and two-photon excitation. The results demonstrate that the HClO level in IBD mice is elevated, and the fast early diagnosis of IBD can be achieved through fluorescence imaging by the proposed Lyso-RS Pdots. This work may provide some solid perspectives for fluorescent diagnosis of H+ and HClO-related diseases.

Turn-On NIR-II Polymer Dots with Large Stokes Shift for In Vivo Visualizing Dynamical Brain Zinc in Alzheimer's Disease Mouse

It is a critical and broad prospect to evaluate ion levels and monitor their dynamic changes in the brain for early diagnosis, in-depth mechanism investigation, and accurate staging of neurodegenerative diseases including Alzheimer's disease (AD). It is still a great challenge to in vivo track Zn2+ levels in the brain by fluorescence imaging due to the drawbacks including short emission wavelength, poor selectivity and sensitivity, and unfavorable penetration across the blood-brain barrier (BBB) for currently developed fluorescent probes. We herein engineer a fluorescent probe with a large Stokes shift of 256 nm, NNDPTQ Pdots, which display substantial Zn2+-specific turn-on response in the NIR II region with the longest emission of 1064 nm up to now. The probe shows a fast response within seconds, high selectivity, low-nanomolar affinity of 6 nM, low detection limit of 3.4 nM, and efficient BBB-permeability efficacy of 37%. The results of brain imaging demonstrate that brain Zn2+ level in AD mice is substantially higher than normal mice and also is elevated with the prolonging of AD-bearing time. This study may provide a promising fluorescent indicator for in vivo tracing of brain Zn2+ levels to reveal AD pathogenesis.

Responsive Theranostic Nanoprobe for Ratiometric Photoacoustic Monitoring of Hypochlorous Acid‐Mediated Inflammation in Cancer Photothermal Therapy

Cancer detection and inflammation monitoring during photothermal therapy (PTT) enable timely cancer intervention and precise inflammation control, advancing to address inflammation‐related tumor recurrence and metastasis associated with PTT. This can be achieved through real‐time monitoring biomarker for cancer and inflammation, like hypochlorous acid (HOCl), a highly reactive oxygen species (hROS) in body with elevated levels in inflammation. Here, a HOCl‐responsive theranostic nanoprobe is introduced, AuNRs@SiO2‐CAA for ratiometric photoacoustic (PA) cancer detection and inflammation monitoring during PTT. AuNRs@SiO2‐CAA emits PA signals at 680 and 820 nm, with only PA680 undergoing changes in the presence of HOCl, enabling precise HOCl imaging via recording changes of ratiometric PA signals (PA680/PA820). AuNRs@SiO2‐CAA exhibits high selectivity and sensitivity, with a detection limit of 0.34 µM for ratiometric PA imaging of HOCl. In vivo, it effectively detects tumor, drives PTT, and monitors inflammation during PTT by sensing HOCl. The successful development of AuNRs@SiO2‐CAA offers a novel theranostic nanoprobe system for cancer diagnosis, poised to enhance PTT through precise inflammation control.

Ratiometric fluorescence imaging of lysosomal NO in living cells and mice brains with Alzheimer's disease

We report an integrated ratiometric lysosomal nitric oxide (NO) nanoprobe based on engineered semiconducting polymer dots (Pdots), LyNO-Pdots, which consist of a newly designed NO-responsive dye, a fluorescent conjugated polymer and two functional polymers. The developed probe LyNO-Pdots exhibit high specificity and stability, good photostability and favorable blood-brain barrier (BBB) penetration ability. The LyNO-Pdots are successfully applied to ratiometric imaging of lysosomal NO variations in brain-derived endothelial cells, brain tissues and mice brains with Alzheimer's disease (AD). The results demonstrate that the NO content in the brains of AD mice is considerably higher than that in normal mice.

A ROS-responsive hydrogel incorporated with dental follicle stem cell-derived small extracellular vesicles promotes dental pulp repair by ameliorating oxidative stress

Pulpitis, an inflammatory disease of dental pulp tissues, ultimately results in the loss of pulp defense properties. Existing clinical modalities cannot effectively promote inflamed pulp repair. Oxidative stress is a major obstacle inhibiting pulp repair. Due to their powerful antioxidative capacity, mesenchymal stem cell-derived small extracellular vesicles (MSC-sEVs) exhibit potential for treating oxidative stress-related disorders. However, whether MSC-sEVs shield dental pulp tissues from oxidative damage is largely unknown. Here, we showed that dental follicle stem cell-derived sEVs (DFSC-sEVs) have antioxidative and prohealing effects on a rat LPS-induced pulpitis model by enhancing the survival, proliferation and odontogenesis of H2O2-injured dental pulp stem cells (DPSCs). Additionally, DFSC-sEVs restored the oxidative/antioxidative balance in DPSC mitochondria and had comparable effects on ameliorating mitochondrial dysfunction with the mitochondrion-targeted antioxidant Mito-Tempo. To improve the efficacy of DFSC-sEVs, we fabricated an intelligent and injectable hydrogel to release DFSC-sEVs by combining sodium alginate (SA) and the ROS sensor RhB-AC. The newly formed SA-RhB hydrogel efficiently encapsulates DFSC-sEVs and exhibits controlled release of DFSC-sEVs in a HClO/ClO- concentration-dependent manner, providing a synergistic antioxidant effect with DFSC-sEVs. These results suggest that DFSC-sEVs-loaded SA-RhB is a promising minimally invasive treatment for pulpitis by enhancing tissue repair in the pulp wound microenvironment.

Semiconducting polymer dots for multifunctional integrated nanomedicine carriers

The expansion applications of semiconducting polymer dots (Pdots) among optical nanomaterial field have long posed a challenge for researchers, promoting their intelligent application in multifunctional nano-imaging systems and integrated nanomedicine carriers for diagnosis and treatment. Despite notable progress, several inadequacies still persist in the field of Pdots, including the development of simplified near-infrared (NIR) optical nanoprobes, elucidation of their inherent biological behavior, and integration of information processing and nanotechnology into biomedical applications. This review aims to comprehensively elucidate the current status of Pdots as a classical nanophotonic material by discussing its advantages and limitations in terms of biocompatibility, adaptability to microenvironments in vivo, etc. Multifunctional integration and surface chemistry play crucial roles in realizing the intelligent application of Pdots. Information visualization based on their optical and physicochemical properties is pivotal for achieving detection, sensing, and labeling probes. Therefore, we have refined the underlying mechanisms and constructed multiple comprehensive original mechanism summaries to establish a benchmark. Additionally, we have explored the cross-linking interactions between Pdots and nanomedicine, potential yet complete biological metabolic pathways, future research directions, and innovative solutions for integrating diagnosis and treatment strategies. This review presents the possible expectations and valuable insights for advancing Pdots, specifically from chemical, medical, and photophysical practitioners' standpoints.

Overcome the "Buckets Effect": Integration of AIEgens into Proteins for Fluorescence-Enhanced Two-Photon Imaging

Luminogens with aggregation-induced emission characteristics (AIEgens) are considered good options for two-photon (2P) probes, owing to their flexibility of design, heavy-metal-free composition, and resistance to photobleaching. However, the design principles for large 2P absorption cross-section (δ) generally require high coplanarity, strong donor-acceptor (D-A) interactions, and long conjugation, which can severely weaken the brightness of AIEgens at the aggregated state and undermine their potential in 2P fluorescence imaging (2PFI). Exploration of a feasible approach to overcome the "Buckets Effect" of AIEgen-based 2P probes is thus a fascinating yet challenging task. Herein, an AIEgen, namely (Z)-2-(4-aminophenyl)-3-(5-(4-(bis(4-methoxyphenyl)amino)phenyl)thiophen-2-yl)acrylonitrile (MTAA) is designed to have a big δ according to the calculation result and a low fluorescence quantum yield (QY) of 2.2% in dimethyl sulfoxide (DMSO). Impressively, upon integrating into bovine serum albumin (BSA), the protein-sized MTAA@BSA dots exhibit a 25-fold higher fluorescence QY compared to MTAA molecules, contributing to an imaging depth of 818 µm in the brain vasculature. The retention and clearance of MTAA@BSA dots in the liver and kidney are also studied using 2PFI. Overall, this work provides a facile approach to overcome the "Buckets Effect" of AIEgen to generate highly efficient, reliable, and biocompatible 2P probes.

Vision for Ratiometric Nanoprobes: In Vivo Noninvasive Visualization and Readout of Physiological Hallmarks

Lesion areas are distinguished from normal tissues surrounding them by distinct physiological characteristics. These features serve as biological hallmarks with which targeted biomedical imaging of the lesion sites can be achieved. Although tremendous efforts have been devoted to providing smart imaging probes with the capability of visualizing the physiological hallmarks at the molecular level, the majority of them are merely able to derive anatomical information from the tissues of interest, and thus are not suitable for taking part in in vivo quantification of the biomarkers. Recent advances in chemical construction of advanced ratiometric nanoprobes (RNPs) have enabled a horizon for quantitatively monitoring the biological abnormalities in vivo. In contrast to the conventional probes whose dependency of output on single-signal profiles restricts them from taking part in quantitative practices, RNPs are designed to provide information in two channels, affording a self-calibration opportunity to exclude the analyte-independent factors from the outputs and address the issue. Most of the conventional RNPs have encountered several challenges regarding the reliability and sufficiency of the obtained data for high-performance imaging. In this Review, we have summarized the recent progresses in developing highly advanced RNPs with the capabilities of deriving maximized information from the lesion areas of interest as well as adapting themselves to the complex biological systems in order to minimize microenvironmental-induced falsified signals. To provide a better outlook on the current advanced RNPs, nanoprobes based on optical, photoacoustic, and magnetic resonance imaging modalities for visualizing a wide range of analytes such as pH, reactive species, and different derivations of amino acids have been included. Furthermore, the physicochemical properties of the RNPs, the major constituents of the nanosystems and the analyte recognition mechanisms have been introduced. Moreover, the alterations in the values of the ratiometric signal in response to the analyte of interest as well as the time at which the highest value is achieved, have been included for most of RNPs discussed in this Review. Finally, the challenges as well as future perspectives in the field are discussed.

Mitochondria-Targeted Ratiometric Chemdosimeter to Detect Hypochlorite Acid for Monitoring the Drug-Damaged Liver and Kidney

Liver and kidney injury caused by drug toxicity is a serious threat to human health. Acetaminophenol (APAP), as a common antipyretic and analgesic drug, inevitably causes injury. When it is overused, hypochlorous acid (HClO) is excessively generated due to metabolic abnormalities, resulting in the accumulation of HClO in the mitochondria of liver and kidney tissues and causing damage. In this study, we designed a series of HClO responsive ratiometric chemdosimeter NRH-X (NRH-O, NRH-S, and NRH-C) to evaluate liver and kidney injury, and found that NRH-O has a specific sensitive response to HClO. NRH-O can not only monitor the variations of endogenous HClO content of living cells by fluorescence ratio changes in the mitochondria but also detect the upregulation of HClO induced by APAP. In addition, NRH-O can also be used for anatomic diagnosis of liver and kidney injury by fluorescence ratio imaging of HClO in the tissues of inflammatory mice.

Boosting the photodynamic therapy of near-infrared AIE-active photosensitizers by precise manipulation of the molecular structure and aggregate-state packing

Organic functional materials have emerged as a promising class of emissive materials with potential application in cancer phototheranostics, whose molecular structures and solid-state packing in the microenvironment play an important role in reactive oxygen species (ROS) generation and the photodynamic therapy (PDT) effect. Clarifying the guidelines to precisely modulate PDT performance from molecular and aggregate levels is desired but remains challenging. In this work, two compounds, TCP-PF6 and TTCP-PF6, with similar skeletons are strategically synthesized, in which a thiophene segment is ingeniously introduced into the molecular backbone of TCP-PF6 to adjust the intrinsic molecular characteristics and packing in the aggregate state. The experimental and theoretical results demonstrate that TTCP-PF6 can form tight packing mode in comparison with TCP-PF6, resulting in efficient cell imaging and enhanced ROS generation ability in vitro and in vivo. The promising features make TTCP-PF6 a superior photosensitizer for PDT treatment against cancer cells by targeting mitochondria. These findings can provide a feasible molecular design for modulating the biological activity and developing photosensitizers with high ROS generation and PDT effect.

Surfactant-free synthesis of fluorescent platinum nanoclusters using HEPES buffer for hypochlorous acid sensing and imaging

A surfactant-free synthesis of noble-metal nanoclusters (NMNCs) with specific function has recently remained more attractive and superior in bio-applications. Herein, by employing the weak reducibility of non-toxic HEPES, we prepared novel water-soluble fluorescent HEPES@Pt NCs by a simple surfactant-free synthesis strategy for hypochlorous acid (HClO) sensing. The as-prepared Pt NCs featured ultra-small size (∼2 nm), bright blue fluorescence, high stability and biocompatibility, and the fluorescence of the Pt NC nanoprobe can be specifically quenched with hypochlorous acid by a static quenching process. Moreover, the surfactant-free Pt NC probe displays fascinating performances for HClO sensing, including fast response to HClO, high stability and specificity, and is further applied for imaging the fluctuations of the HClO concentration in living cells with satisfactory results for the first time. Thereby, we anticipate that it is a reliable and attractive approach to develop versatile NMNCs through the surfactant-free synthesis for further applications in biological research.

Green-emitting carbon quantum dots as a dual-mode fluorescent and colorimetric sensor for hypochlorite

In this work, green-emitting carbon quantum dots were successfully prepared through a facile one-step solid-state reaction method. The obtained green-emitting carbon dots (G-CDs) showed good fluorescence stability in NaCl aqueous solution and different pH values. Moreover, the G-CDs showed high sensitivity and selectivity for detecting hypochlorite by both fluorometry and colorimetry. Under the optimized condition, a highly sensitive detection of hypochlorite was established in the range of 0.2-100 μM and 10-150 μM for fluorescent and colorimetric methods, respectively. The corresponding limits of detection (LOD) were 0.0781 μM and 1.82 μM, respectively. Therefore, the G-CDs were successfully applied to determinate hypochlorite in actual water samples. In addition, a paper-based sensor loading with the G-CDs was also developed for rapid visual detection of hypochlorite. The results suggested that the G-CDs could be a promising candidate to detect hypochlorite.

A pyrene-pyridyl nanooligomer as a methoxy-triggered reactive probe for highly specific fluorescence assaying of hypochlorite

A novel pyrene-pyridyl conjugated oligomer (OPP-OMe) was conveniently prepared by one-pot Sonogashira coupling. Intriguingly, it was found that introducing only one methoxy moiety at the 4-pyridyl position can be sufficient for creating an oligomer-based ultrafine reactive fluorescent nanoprobe, i.e., OPP-OMe NPs (ca. 2.5 nm in diameter). Spectral analyses and elucidation of the intermediate structure revealed that the methoxy triggered-oxidation, together with nanoaggregation of OPP-OMe NPs, results in rapid, specific and supersensitive sensing of hypochlorite (LOD, 0.3 nM, S/N = 3).

Preparation, characterization and cell labelling of strong pH-controlled bicolor fluorescence carbonized polymer dots

As a class of important carbon nanomaterial, carbonized polymer dots (CPDs), also called carbon dots (CDs), have aroused wide interest owing to their unique water solubility, fluorescence properties, and rich surface functional groups. However, the directional tuning of the fluorescence properties of CPDs remains incomplete because of the influence of many factors like diameter, solvent and surface groups. Particularly, most carbonized polymer dots are synthesized in a neutral pH environment. Herein, by modulating the pH (strongly acidic or alkaline) of dextrin water solution, bicolor fluorescence emission (blue and yellow) CPDs were prepared by a hydrothermal reaction. Through systematic characterization, it was found that the different fluorescence properties are regulated by the diameters and surface groups of the carbon cores. Simultaneously, the pH value affected the nucleation process. Based on the excellent fluorescence properties, cell fluorescence imaging and cytotoxicity were tested. The bicolor fluorescence CPDs obtained by tuning the pH provide an important theoretical basis for the design of broadband CPDs.

Conjugated Polymers-based Luminescent Probes for Ratiometric Detection of Biomolecules

Accurate monitoring of the biomolecular changes in biological and physiological environments is of great significance for pathogenesis, development, diagnosis and treatment of diseases. Compared with traditional luminescent probes on the...