Switch-on near infrared emission in albumin behind dark fabric: toward application in forensic latent bloodstain detection

Latent bloodstain detection remains imperative for crime scene investigators. Widely used luminol offers high sensitivity to human blood, but can produce untrustworthy results from a bleach-cleaned crime scene or in a room not dark enough. Furthermore, dark pigments impede imaging bloodstains covered by dark materials with previously reported bloodstain detection agents. A novel on/off human albumin-sensing dye (SO3C7) is reported herein with a longer emission wavelength (942 nm) than previous materials that allows imaging behind ∼5 mm of black fabric. The switch-on emission of SO3C7 is selective and sensitive to human albumin and lasts longer than luminol (24-48 hours). Emission studies, transient absorption spectra (TAS), and near-infrared (NIR) photographs herein describe the albumin sensing properties of the dye.

A fluorescent probe based on the ESIPT (excited state intramolecular proton transfer) mechanism for rapid detection of endogenous and exogenous H2O2 (hydrogen peroxide) in cells

Hydrogen peroxide (H2O2) is one of the important reactive oxygen species in the body and can be used as a marker of some diseases such as cancer and neurodegenerative diseases. Therefore, it is of great significance to develop fluorescent probes that can detect H2O2 in living organisms for early diagnosis of diseases. However, slow response time and low fluorescence quantum yield limit the application of many probes. In this study, using 2-(2-hydroxyphenyl) benzothiazole (HBT) as the fluorophore, the introduction of weakly absorbing bromine atoms can accelerate the speed of electron transfer during the recognition process. Three ESIPT (excited state intramolecular proton transfer) fluorescent probes JLO/JLM/JLP were designed and synthesized. The detection of H2O2 can be achieved with all three probes, and we screened a probe JLO with the fastest response time (30 min) and highest fluorescence quantum yield (Ф = 0.731). The probe also has a large Stokes shift, which can reduce fluorescence self-absorption and background interference, and also has a high sensitivity, which is designed to accurately detect endogenous and exogenous H2O2 in living cells, which has great potential for biological applications.

Catechin-Albumin Conjugates: Enhanced Antioxidant Capacity and Anticancer Effects

(+)-Catechin conjugated with human serum albumin (CT–HSA) was prepared and evaluated as a drug carrier bearing anticancer effects. It was found that 2.4 mol of CT was conjugate to 1 mol HSA. The CT–HSA has an antioxidant capacity of about 3.3 times the amount of CT in the conjugate. Intracellular incorporation of the CT–HSA was analyzed by fluorescence-activated cell sorting (FACS) and confocal laser scanning microscopy (CLSM) measurements using fluorescein isothiocyanate (FITC)-labelled CT–HSA. The results indicated that the FITC-labelled CT–HSA was incorporated into HeLa cells in a concentration-dependent manner. The CT–HSA enhanced the binding of anticancer drugs (5-fluorouracil (5-Fu) and mitomycin C (MMC)) comparing with HSA, and the CT–HSA mixed with 5-Fu or MMC decreased significantly the HeLa cell viability as compared with the same concentration of each drug. In addition, intracellular reactive oxygen species (ROS) scavenging by the CT–HSA is likely to affect the anticancer effects. Thus, the CT–HSA enhanced anticancer drug efficacy in relation to controlling ROS-scavenging ability.

Rational design of a fluorescent probe for specific sensing of hydrogen peroxide/glucose and intracellular imaging applications

A new type of dye with advantages of high selectivity and sensitivity is formed by using the strategy of hybridization between the luminescent unit and recognition unit. Based on this strategy, we exploit a novel dye bonding the benzopyrylium salt as a luminescent unit and phenylboronate group as a response site, which is served as a fluorescent probe 1 for specific recognition of hydrogen peroxide in biological application. Probe 1 employs a unique recognition switch, phenylboronate unit, to"turn-on"a highly specific and rapid fluorescence response toward hydrogen peroxide combined with the 1,6-rearrangement elimination reaction strategy. Meanwhile, probe 1 has the ability to glucose assay by taking advantage of glucose oxidase/glucose enzymatic reaction. What's more, the probe 1 is capable of tracking endogenous hydrogen peroxide in living cells and intracellular imaging. Therefore, the newly developed bioprobe 1 is expected to be used to monitor hydrogen peroxide and glucose levels in complex organisms.

Fluorescence detection and imaging of intracellular sulphite using a remote light activatable photochromic nanoprobe

The development of a responsive fluorescent probe for the detection of a particular biomolecule in a specific site at the desired moment is important in the fields of bioanalysis and imaging, molecular biology and biomedical research. In this work, we report the development of a remote-light activatable nanoprobe for the fluorescence detection of sulphite in pure aqueous solution and its imaging applications in living cells. The nanoprobe, Poly-Cm-SP, is fabricated simply by wrapping photochromic molecules (Cm-SP) into a polymer nanoparticle. Upon alternate UV/Vis light irradiation for several seconds, the Poly-Cm-SP nanoprobe exhibits red/blue fluorescence switch due to the inactive/active FRET processes from coumarins to the SP/MR isomers of the photochromic molecule. In the presence of sulphite, the specific reaction of sulphite with the electron deficit "CC" bond of the MR isomer occurs, resulting in an inefficient FRET process and thus exhibiting a constant "ON" blue channel fluorescence signal. After UV-light irradiation, the formation of activated Poly-Cm-MRin situ thus enables the detection of sulphite through recording the ratiometric changes of fluorescence signals at both blue and red channels. The Poly-Cm-SP nanoprobe possesses excellent biocompatibility and lysosome distribution capability, allowing it to be used for photochromic imaging and sulphite detection in the lysosomes of living macrophage cells. This work thus offers a new remote-light activatable nanoprobe for the detection and imaging of sulphite in biological systems.

A near-infrared fluorescent probe based on the hemicyanine skeleton for the detection of hydrogen peroxide in vivo

As a member of the reactive oxygen species, hydrogen peroxide (H₂O₂) plays critical roles in oxidative stress and cell signaling. Intracellular abnormal levels of H₂O₂ production are closely related to many diseases. Therefore, the real-time monitoring of H₂O₂ in the cells is important. In this work, we designed a novel fluorescent probe (Mito-H₂O₂) for the specific detection of H₂O₂ based on the hemicyanine skeleton, with bright near-infrared fluorescence emission. Mito-H₂O₂ displayed fast response, excellent water-solubility and great fluorescence intensity enhancement after the addition of H₂O₂. Furthermore, Mito-H₂O₂ has been successfully applied to image both of the exogenous and endogenous H₂O₂ in cells and mice with negligible cytotoxity.

A mitochondria-targeted fluorescent probe for real-time imaging SO2/H2O2

Studies have shown that changes in the redox state of cells might be closely related to pathological and physiological processes. Sulfur dioxide and hydrogen peroxide, as a significant redox couple in living cells, are endogenously produced by cells. Here, we report a long-wavelength fluorescent probe to reversibly monitor sulfur dioxide and hydrogen peroxide. This probe (NBD) displayed high selectivity and sensitivity, which could be accumulated in mitochondria for real-time imaging of SO₂/H₂O₂. These results indicated that NBD would be an ideal tool for monitoring the redox cycle state in living cells.

A carbon dots functionalized paper coupled with AgNPs composites platform: application as a sensor for hydrogen peroxide detection based on surface plasmon-enhanced energy transfer

A paper-based fluorescent sensor (PCD/AgNPs) consisted of CDs functionalized paper and AgNPs was developed for sensing H₂O₂ in milk samples and cancer cells.

Alizarin-based molecular probes for the detection of hydrogen peroxide and peroxynitrite

Phenol fluorophores are a large family of fluorophores, which have attracted more and more attention in the design of probes.

Resorufin-based responsive probes for fluorescence and colorimetric analysis

The fluorescence imaging technique has attracted increasing attention in the detection of various biological molecules in situ and in real-time owing to its inherent advantages including high selectivity and sensitivity, outstanding spatiotemporal resolution and fast feedback. In the past few decades, a number of fluorescent probes have been developed for bioassays and imaging by exploiting different fluorophores. Among various fluorophores, resorufin exhibits a high fluorescence quantum yield, long excitation/emission wavelength and pronounced ability in both fluorescence and colorimetric analysis. This fluorophore has been widely utilized in the design of responsive probes specific for various bioactive species. In this review, we summarize the advances in the development of resorufin-based fluorescent probes for detecting various analytes, such as cations, anions, reactive (redox-active) sulfur species, small molecules and biological macromolecules. The chemical structures of probes, response mechanisms, detection limits and practical applications are investigated, which is followed by the discussion of recent challenges and future research perspectives. This review article is expected to promote the further development of resorufin-based responsive fluorescent probes and their biological applications.