Photoactivatable (alternatively, photoremovable, photoreleasable, or photocleavable) protecting groups (PPGs), also known as caged or photocaged compounds, are used to enable non-invasive spatiotemporal photochemical control over the release of species of interest. Recent years have seen the development of PPGs activatable by biologically and chemically benign visible and near-infrared (NIR) light. These long-wavelength-absorbing moieties expand the applicability of this powerful method and its accessibility to non-specialist users. This review comprehensively covers organic and transition metal-containing photoactivatable compounds (complexes) that absorb in the visible- and NIR-range to release various leaving groups and gasotransmitters (carbon monoxide, nitric oxide, and hydrogen sulfide). The text also covers visible- and NIR-light-induced photosensitized release using molecular sensitizers, quantum dots, and upconversion and second-harmonic nanoparticles, as well as release via photodynamic (photooxygenation by singlet oxygen) and photothermal effects. Release from photoactivatable polymers, micelles, vesicles, and photoswitches, along with the related emerging field of photopharmacology, is discussed at the end of the review.

Visible-to-NIR-Light Activated Release: From Small Molecules to Nanomaterials.

Metal-coordinated fluorescent and luminescent probes for reactive oxygen species (ROS) and reactive nitrogen species (RNS)

Food fermentation, antibiotics, and pollutant degradation are closely related to bacteria. Bacteria play an irreplaceable role in life. However, some bacteria seriously threaten human health and cause large-scale infectious diseases. Therefore, there is a pressing need to develop strategies to accurately monitor bacteria. Technology based on molecular probes and fluorescence imaging is noninvasive, results in little damage, and has high specificity and sensitivity, so it has been widely applied in the detection of bacteria. In this review, we summarize the recent progress in bacterial detection using fluorescence. In particular, we generalize the mechanisms commonly used to design organic fluorescent probes for detecting and imaging bacteria. Moreover, a perspective regarding fluorescent probes for bacterial detection is discussed.

Recent progress in fluorescent probes for bacteria.

A fluorescent probe for the monitoring of H2S levels in living cells and organisms is highly desirable. In this regard, near-infrared (NIR) fluorescent probes have emerged as a promising tool. NIR-I and NIR-II probes have many significant advantages; for instance, NIR light penetrates deeper into tissue than light at visible wavelengths, and it causes less photodamage during biosample analysis and less autofluorescence, enabling higher signal-to-background ratios. Therefore, it is expected that fluorescent probes having emission in the NIR region are more suitable for in vivo imaging. Consequently, a considerable increase in reports of new H2S-responsive NIR fluorescent probes appeared in the literature. This review highlights the advances made in developing new NIR fluorescent probes aimed at the sensitive and selective detection of H2S in biological samples. Their applications in real-time monitoring of H2S in cells and in vivo for bioimaging of living cells/animals are emphasized. The selection of suitable dyes for designing NIR fluorescent probes, along with the principles and mechanisms involved for the sensing of H2S in the NIR region, are described. The discussions are focused on small-molecule and nanomaterials-based NIR probes.

Sensing and Bioimaging of the Gaseous Signaling Molecule Hydrogen Sulfide by Near-Infrared Fluorescent Probes.

Sulfite (SO32−) and bisulfite (HSO3−) have been widely used in food preservation to avoid oxidation and microbe growth and inhibit enzymatic reactions. Extensive intake of SO32−/HSO3− will cause allergic reactions and even tissue damages in some individuals. Therefore, developing responsive small-molecule probes for rapid, effective, and quantitative detection of SO32−/HSO3− in various foods has attracted increasing attentions in recent years. Based on different response mechanisms, such as nucleophilic addition with the electron deficit “C C” bonds, ketone or aldehyde groups, and inhibition of C N isomerization, a number of responsive small-molecule probes have been developed for food analysis. This review focuses on the progress in the development of responsive small-molecule probes for SO32−/HSO3− analysis in food samples. Their chemical structures, response mechanisms with SO32−/HSO3−, and performance for SO32−/HSO3− analysis in food samples are summarized and discussed. The future research directions for developing novel probes for SO32−/HSO3− analysis in food samples are proposed.

Responsive small-molecule luminescence probes for sulfite/bisulfite detection in food samples

Fluorescent nanoprobes for the sensing of gasotransmitters hydrogen sulfide (H2S), nitric oxide (NO) and carbon monoxide (CO).

Nanoscale vesicles functionalized with a nitric oxide (NO) releasing molecule 4-nitro-3-(trifluoromethyl)aniline have been reported. The new NO-nano-vesicular donor material shows an effective photo-release of NO upon irradiation with blue light at 410 nm. The kinetics of NO release has been monitored by using simple spectroscopic techniques such as UV-Vis and fluorescence methods. Colorimetric Griess assay and fluorescence DAF assay have been used for the detection and quantification of NO released from vesicles. This new vesicular nanoscale NO donor has the advantages of facile preparation in water, capable of releasing NO in a pure aqueous medium, photo-controlled NO release, bio-compatibility and capacity to modulate the NO donor loading to achieve an essential amount of NO.

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Nanoscale lipid vesicles functionalized with a nitro-aniline derivative for photoinduced nitric oxide (NO) delivery

Incorporating water-insoluble nitric oxide (NO)-releasing molecules into biocompatible vesicles may allow for the tunable control of NO release on a specific target site. In vesicles, membrane fluidity plays an important role and influences the final therapeutic efficiency of drugs loaded into the vesicles. Hence, we aimed to investigate the effect of lipid fluidity on the NO release behavior of the photo-controllable ruthenium nitrosyl (Ru-NO) complex. In this regard, a new photoactive ruthenium nitrosyl complex (L.Ru-NO) with amphiphilic terpyridine ligand was synthesized and characterized in detail. L.Ru-NO was incorporated with commercial phospholipids to form nanoscale vesicles L.Ru-NO@Lip. The photoactive {Ru-NO}6 type complex released NO in the organic solvent CH3CN and aqueous liposome solution by irradiating under low-intensity blue light (λ = 410 nm, 3 W). To demonstrate the effect of lipid structure and fluidity on NO release, four different liposome systems L.Ru-NO@Lip1-4 were prepared by using phospholipids such as DOPC, DSPC, DPPC, and DMPC having different chain lengths and saturation. The NO-releasing abilities of these liposomes in aqueous medium were studied by UV-vis spectrum, colorimetric Greiss, and fluorescent DAF assay. The results show that the rate of NO release could be easily tuned by varying the lipid fluidity. The effect of temperature and pH on NO release was also studied. Further, the complex L.Ru-NO and liposomes L.Ru-NO@Lip1 were assayed as an antibacterial agent against the strains of bacteria Escherichia coli and Staphylococcus aureus.

Regulation of Nitric Oxide (NO) Release by Membrane Fluidity in Ruthenium Nitrosyl Complex-Embedded Phospholipid Vesicles.

A liposome based nanosensor Lipo-1 for efficient detection of copper, cyanide (CN-) and ATP in a pure aqueous medium has been described. Lipo-1 shows a fluorescence ON-OFF response with copper. However, Lipo-1.Cu (Lipo-1 and copper ensemble) was used for the OFF-ON detection of ATP with nM and CN- with μM detection levels, lower than the WHO permissible level for safe drinking. Lipo-1 has better and enhanced binding properties over the counter organic amphiphilic compound Bzimpy-LC, which is not soluble in water. The significant changes in the emission spectra in the presence of Cu2+, CN- and ATP ions, as variable inputs, are used to construct INHIBIT and OR logic operations in a nano-scale environment. The fluorescent detection of CN- ions with Lipo-1.Cu was used to develop an enzyme assay for β-glucosidase using amygdalin as the substrate. β-Glucosidase enzymatic activity was monitored by the emission OFF-ON signal of the probe Lipo-1.Cu by CN- detection. This approach could be an efficient method for developing a fluorescence-based β-glucosidase enzyme assay. A switch ON luminescence response, low detection limit, fast response, 100% aqueous solution, biocompatibility, multi-analyte detection, and improved sensitivity and selectivity of Bzimpy-LC in lipid bilayer membranes are the main features of the nanoprobe Lipo-1. These properties give it a clear advantage for analytical applications.

Nancy Sharma

Papers

Sensing and Bioimaging of the Gaseous Signaling Molecule Hydrogen Sulfide by Near-Infrared Fluorescent Probes.

Fluorescent nanoprobes for the sensing of gasotransmitters hydrogen sulfide (H2S), nitric oxide (NO) and carbon monoxide (CO).

Nanoscale lipid vesicles functionalized with a nitro-aniline derivative for photoinduced nitric oxide (NO) delivery

Regulation of Nitric Oxide (NO) Release by Membrane Fluidity in Ruthenium Nitrosyl Complex-Embedded Phospholipid Vesicles.

Multi analyte sensing of amphiphilic tridentate bis(benzimidazolyl)pyridine incorporated in liposomes and potential application in enzyme assay.