Luminescence Nanoprobe in the Near-Infrared-II Window for Ultrasensitive Detection of Hypochlorite

Construction of CDs@β-CD@CCM ratiometric fluorescence probe for FRET-based ClO--sensing

β-Cyclodextrin (β-CD)-functionalized carbon quantum dots (CDs) loaded with curcumin (CCM) were used for ClO-sensing with high sensitivity and selectivity. This fluorescence resonance energy transfer (FRET)-based sensor was created through attaching CCM to the CDs via β-CD linker. CCM could get into the interior of β-CD triggering the FRET from CDs to CCM, providing an 'off' state of the CDs. However, the effect of FRET was weakened by the ClO-, because the o-methoxyphenol structure from CCM was oxidized to be benzoquinone. The fluorescence intensity of CDs@β-CD@CCM at 440 nm can be heightened and 520 nm from CCM can decrease along with the increased ClO-. Therefore, a ratiometric fluorescence probe for ClO-sensing is successfully constructed. It conforms to a polynomial curve equation which is I440/I520= -0.0268 + 0.0315 CClO-+ 0.0055[CClO-]2(R2= 0.9958) between 0 and 18.4μM ClO-. Furthermore, we also obtain excellent results using this spectrophotometric method for ClO--sensing in pure water and commercial disinfectants, which afford potential in the environment monitoring area. We expect this sensing platform could be helpful in other analogous probes in relevant fields.

NIR-II Fluorescence Sensor Based on Steric Hindrance Regulated Molecular Packing for In Vivo Epilepsy Visualization

Fluorescence sensing is crucial to studying biological processes and diagnosing diseases, especially in the second near-infrared (NIR-II) window with reduced background signals. However, it's still a great challenge to construct "off-on" sensors when the sensing wavelength extends into the NIR-II region to obtain higher imaging contrast, mainly due to the difficult synthesis of spectral overlapped quencher. Here, we present a new fluorescence quenching strategy, which utilizes steric hindrance quencher (SHQ) to tune the molecular packing state of fluorophores and suppress the emission signal. Density functional theory (DFT) calculations further reveal that large SHQs can competitively pack with fluorophores and prevent their self-aggregation. Based on this quenching mechanism, a novel activatable "off-on" sensing method is achieved via bio-analyte responsive invalidation of SHQ, namely the Steric Hindrance Invalidation geNerated Emission (SHINE) strategy. As a proof of concept, the ClO--sensitive SHQ lead to the bright NIR-II signal release in epileptic mouse hippocampus under the skull and high photon scattering brain tissue, providing the real-time visualization of ClO- generation process in living epileptic mice.

N-aminomorpholine-functionalized bromine-doped carbon dots for hypochlorous acid detection in foods and imaging in live cells

Hypochlorous acid (HClO) is used in food preservation. However, excessive HClO can deteriorate nutritional composition of food, compromise its quality, and potentially induce various diseases. Consequently, the development of multifunctional fluorescent probes for the sensitive and selective detection of HClO is highly anticipated for food safety. In this work, we designed a nanoprobe using N-aminomorpholine (AM)-functionalized bromine-doped carbon dots (Br-CDs-AM) for sensing HClO. This nanoprobe exhibits pH stability, strong resistance to photobleaching, superior long-term photostability (12 weeks), high sensitivity (19.3 nM), and an ultrarapid response (8 s) for detecting HClO residues in food matrices with percentage recovery (96.5 %-108 %) and RSDs less than 5.34 %. In addition, extremely low cytotoxicity and outstanding biocompatibility enable the nanoprobe to be used primarily for lysosome tracking and rapidly visualizing HClO in live cells. Thus, this study provides a new pathway to design unconventional nanoprobes for food safety assessment and subcellular organelle-specific imaging HClO.

A novel fluorescent probe based on carbazole-thiophene for the recognition of hypochlorite and its applications

A carbazole thiophene-aldehyde and 4-methylbenzenesulfonhydrazide conjugate CSH was synthesized by introducing 5-thiophene aldehyde at the 3-position of the carbazole group as the precursor and then condensing it with 4-methylbenzenesulfonhydrazide. CSH has high selectivity and sensitivity towards ClO-, which can specifically identify ClO- by UV-Vis and fluorescence spectroscopy. CSH can rapidly respond to ClO- in the physiological pH range through a fluorescence quenching pattern, accompanied by the color of CSH changing markedly from turquoise to yellowish green under the 365 nm UV light. Probe CSH exhibits a quantitative response to ClO- (0-11 μM) with a low detection limit (1.16 × 10-6 M). Cell imaging experiments have shown that CSH can capture fluorescent signals in the cyan and yellow channels of HeLa cells through fluorescence confocal microscopy, and can successfully identify exogenous ClO- in HeLa cells. In addition, probe CSH can also be used to detect ClO- in environmental water samples. These results indicate that CSH has potential application prospects in the environmental analysis and biological aspects.

Preparation of SERS base membrane with cellulose compound dopamine and determination of hypochlorite

Flexible silver substrates were made by in situ reduction of silver nanoparticles in bacterial cellulose membranes using the unique advantage of dopamine. Subsequently, we modified the substrate with 4-mercaptophenol (4-MP), a molecule capable of specifically recognizing ClO-, and its corresponding SERS signal changes with the concentration of hypochlorite, thus allowing the quantitative detection of ClO- content. The method showed a negative linear correlation (R2 = 0.9567) with the SERS intensity at 1077 cm-1 over the concentration range 0.5-100 µM, and the detection limit was 0.15 µM. The RSD of the SERS intensity at 1077 cm-1 under five batches was 4.2%, which proved the good reproducibility of P-BCM-Ag NP-MP. Finally, the P-BCM-Ag NPs were used for the detection of hypochlorite in cell contents, artificial urine, and clinical serum samples, utilizing spike experiments in all three environments. The recoveries were in the range 90-110% indicating the accuracy of the method for the detection of hypochlorite and validating the promising application of this assay for practical detection in intricate biological samples.

Hypochlorous acid-activated near-infrared fluorescent probe for in vivo/exogenous detection and dairy toxicity evaluation

Oxidative stress has been reported to be closely associated with many diseases, and an excessive overdose of hypochlorite (ClO^-) can also induce stress-related diseases. In this study, we designed and synthesized a NIR probe, named W-1a based on computational analysis of DCM (4-(Dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran) derivatives for specific detection of ClO^-. The probe exhibited dual fluorescence and colorimetric sensing with a response time of <1 min and a detection limit of 0.15 μM. Additionally, the probe was successfully applied for fluorescence imaging of ClO^- at the cellular level and ebrafish endogenous/exogenous ClO^- assay and dairy toxicity assessment. Thus, we present a potential method for developing an efficient and reliable detection of ClO^- in early stage using near-infrared dyes.

Engineering a polymer-encapsulated manganese dioxide/upconversion nanoprobe for FRET-based hydrogen peroxide detection

Hydrogen peroxide (H₂O₂) is considered a significant biomarker in various diseases and could induce deleterious health problems at irregular physiological concentrations. Therefore, developing a simple, efficient biocompatible nanoprobe for trace amount H₂O₂ detection with high sensitivity and specificity is of great help for early diagnosis and therapeutics. Herein, we designed amphiphilic poly(styrene-co-maleic anhydride) (PMSA)-encapsulated nanoclusters composed of upconversion nanoparticles (UCNPs) and manganese dioxide nanoparticles (MnO₂ NPs) at a specific ratio to produce a near-infrared (NIR) excited luminescent nanoprobe for H₂O₂ detection. Our results revealed that the MnO₂ NPs tended to experience catalytic decomposition when exposed to H₂O₂, while the UCNPs were retained inside the PSMA encapsulation, causing recovery of the UCNP emission band at 470 nm in accordance with H₂O₂ concentration. This luminescence recovery was linearly dependent on H₂O₂ concentrations, yielding a limit of detection (LOD) of 20 nM. The easy-to-interpret H₂O₂ nanoprobe also proved high selectivity in the presence of other interfering substances, and biocompatibility and water-dispersibility, making it an ideal candidate for real-time detection of disease-related H₂O₂ in living organisms.

3-Aminophenylboronic acid-functionalized molybdenum disulfide quantum dots for fluorescent determination of hypochlorite

A simple method is reported for hypochlorite determination based on fluorescence 3-aminophenylboronic acid-functionalized molybdenum disulfide quantum dots (B-MoS₂ QDs). B-MoS₂ QDs with strong fluorescence at 380 nm have been successfully synthesized by the amidation reaction between APBA and hydrothermal MoS₂ QDs. Hypochlorite sensing was proposed utilizing the fluorescent quenching effect of 3,3',5,5'-tetramethylbenzidine dihydrochloride (TMB) on B-MoS₂ QDs and the fast redox reaction between hypochlorite and TMB. The fluorescent quenching effect of TMB to B-MoS₂ QDs was proved to be caused by static dynamic quenching and inner filter effect. A good linear relationship was obtained in the hypochlorite concentration range from 1 to 20 μM, and the limit of detection (LOD) was 36.8 nM. The proposed fluorescent detection assay was simple and fast, taking only 5 min at room temperature. Satisfactory results were obtained in the standard spike recovery tests on tap water and milk samples, which indicate high potential in constructing fluorescent bio-detection assays.

Tumor microenvironment enhanced NIR II fluorescence imaging for tumor precise surgery navigation via tetrasulfide mesoporous silica-coated Nd-based rare-earth nanocrystals

In vivo fluorescent imaging by using the new contrast agents emitted at short-wavelength infrared region (NIR II, 1000–1700 ​nm) presents an unprecedent advantages in imaging sensitivity and spatial resolution over traditional near-infrared (NIR) light. Recently, Nd-based rare-earth nanocrystals have attracted considerable attention due to the high quantum yield (∼40%) of their emission at NIR II. However, undesirable capture by reticuloendothelial system to bring strong background signal is unsatisfying for tumor discrimination. Here, GSH-sensitive tetrasulfide bond incorporated mesoporous silica shell has entrusted onto Nd-based down-conversion nanocrystals (DCNPs) surface to totally quench the fluorescence of DCNPs. After RGD conjugation on the silica surface, the NIR II contrast agents could actively target to liver tumors. Then tetrasulfide bonds can be broken during the silica framework decomposing in cytoplasm under high GSH concentration to result in NIR II fluorescence explosive recover. Benefiting from this specific response under tumor microenvironment, the NIR II signal in other organs was markedly reduced, while the signal-to-background ratio is prominently enhanced in tumors. Then, solid liver tumors were successfully resected under the guidance of our GSH responsive NIR II fluorescent imaging with no recurrence after 20-day of surgery. Meanwhile, by combining with the ignorable side effects, the Nd-based nanoprobes vastly improved the imaging resolution of tumor margin, opening a paradigm of NIR II fluorescent imaging-guided surgery.

Lysosome-targetable brightly green fluorescence carbon dots for real-time monitoring in cell and highly efficient removal in environment of hypochlorite

Due to the lacks of lysosome localization group and reaction/interaction site for hypochlorite (ClO^-) on the surface of the carbon dots (C-dots), no C-dots-based lysosome-targeted fluorescence probes have, so far, been reported for real-time monitoring intracellular ClO^-. In this work, 1,3,6-trinitropyrene (TNP) was used as a precursor to prepare C-dots with maximum excitation and emission wavelengths at 485 and 532 nm, respectively, and quantum yield ∼ 27% by a hydrothermal approach at 196 °C for 6 h under a reductive atmosphere. The brightly green C-dots can sensitively and quickly respond to ClO^- in aqueous solution through surface chemical reaction, showing a linear relationship in the range of 0.5-120 μΜ ClO^- with 0.27 μΜ of limit of detection (LOD). Most significantly, the C-dots can localize at intracellular lysosome to image ClO^- in lysosomes. Also, the magnetic nanocomposites (C-dots@Fe₃O₄ MNCs) were fabricated via a simple electrostatic self-assembly between Fe₃O₄ magnetic nanoparticles (Fe₃O₄ MNPs) and C-dots for highly efficient removal of ClO^- in real samples. Therefore, lysosome-targetable C-dots-based probes for real-time monitoring ClO^- were successfully constructed, opening up a promising door to investigate the biological functions and pathological roles of ClO^- at organelle levels.

Aggregation-Induced Emission Fluorophore-Incorporated Curcumin-Based Ratiometric Nanoprobe for Hypochlorite Detection in Food Matrices

The development of efficient, economic, reliable, and accurate monitoring of hypochlorite (ClO^-) in food matrices is in great demand for food safety assessment, particularly during its massive use against the COVID-19 epidemic. Here, we prepared an aggregation-induced emission (AIE) fluorophore tetraphenylethylene (TPE)-incorporated curcumin-based hybrid ratiometric fluorescence nanoprobe (Curcumin/TPE@HyNPs) through amphiphilic phospholipid polymer-powered nanoprecipitation, which exhibited a fast, highly sensitive, and selective response to the residual ClO^- in real food matrices. Because of the inner filter effect (IFE) from curcumin toward TPE inside the nanoprobe, the bright fluorescence of TPE aggregation at ∼437 nm was effectively quenched, along with an enhanced fluorescence of curcumin at ∼478 nm. Once there was a ClO^- residue in food matrices, ClO^- triggered the oxidation of o-methoxyphenol inside curcumin and led to the almost complete absorption collapse, thereby terminating curcumin fluorescence at ∼478 nm and the IFE process. Accordingly, the fluorescence of TPE at ∼437 nm was recovered. In this case, a ratiometric fluorescent response of Curcumin/TPE@HyNPs toward the residual ClO^- in food matrices (e.g., milk) was proposed with a low detection limit of 0.353 μM and a rapid response time of 140.0 s. Notably, the phospholipid polymer as the protection layer effectively reduced/evaded the nonspecific binding of signal reporters inside the nanoprobe, facilitating it to directly monitor the residual ClO^- in real food matrices. This work provided a novel approach to utilize the unconventional AIE luminophors for constructing the efficient and reliable early warning mechanisms toward various food contaminants.

Management of fluorescent organic/inorganic nanohybrids for biomedical applications in the NIR-II region

Biomedical fluorescence imaging in the second near-infrared (NIR-II, 100-1700 nm) window provides great potential for visualizing physiological and pathological processes, owing to the reduced tissue absorption, scattering, and autofluorescence. Various types of NIR-II probes have been reported in the past decade. Among them, NIR-II organic/inorganic nanohybrids have attracted widespread attention due to their unique properties by integrating the advantages of both organic and inorganic species. Versatile organic/inorganic nanohybrids provide the possibility of realizing a combination of functions, controllable size, and multiple optical features. This tutorial review summarizes the reported organic and inorganic species in nanohybrids, and their biomedical applications in NIR-II fluorescence and lifetime imaging. Finally, the challenges and outlook of organic/inorganic nanohybrids in biomedical applications are discussed.