A selective sensor 1 for the fluorescent imaging of Cd2+ in living cells has been designed and synthesized based on an internal charge transfer (ICT) mechanism. It can distinguish Cd2+ from Zn2+ and can be used in both general fluorescence intensity microscopy and ratiometric fluorescence microscopy.

Intracellular viscosity strongly influences transportation of mass and signal, interactions between the biomacromolecules, and diffusion of reactive metabolites in live cells. Fluorescent molecular rotors are recently developed reagents used to determine the viscosity in solutions or biological fluid. Due to the complexity of live cells, it is important to carry out the viscosity determinations in multimode for high reliability and accuracy. The first molecular rotor (RY3) capable of dual mode fluorescence imaging (ratiometry imaging and fluorescence lifetime imaging) of intracellular viscosity is reported. RY3 is a pentamethine cyanine dye substituted at the central (meso-) position with an aldehyde group (CHO). In nonviscous media, rotation of the CHO group gives rise to internal conversion by a nonradiative process. The restraining of rotation in viscous or low-temperature media results in strong fluorescence (6-fold increase) and lengthens the fluorescence lifetime (from 200 to 1450 ps). The specially designed molecular sensor has two absorption maxima (λ(abs) 400 and 613 nm in ethanol) and two emission maxima (in blue, λ(em) 456 nm and red, 650 nm in ethanol). However it is only the red emission which is markedly sensitive to viscosity or temperature changes, providing a ratiometric response (12-fold) as well as a large pseudo-Stokes shift (250 nm). A mechanism is proposed, based on quantum chemical calculations and (1)H NMR spectra at low-temperature. Inside cells the viscosity changes, showing some regional differences, can be clearly observed by both ratiometry imaging and fluorescence lifetime imaging (FLIM). Although living cells are complex the correlation observed between the two imaging procedures offers the possibility of previously unavailable reliability and accuracy when determining intracellular viscosity.

Conventional cancer chemotherapy is often associated with toxicity issues. Thus, new drug delivery systems (DDSs) are developed as alternatives owing to their potential to selectively target affected cells while sparing normal tissues. Among them, noninvasive and biocompatible mesoporous silica nanoparticle (MSN)-based targeted DDSs have developed rapidly. In particular, controlled gatekeepers capping the pore entrances of MSNs play prominent and crucial roles in achieving specific drug release and avoiding premature leakage in the delivery process before the target is reached, and perfect gatekeepers can only be removed under specific internal or external stimuli, such as pH, redox potential, temperature, biomolecules, light, magnetic field and ultrasound, or a combination of these stimuli, which is significant for precise therapeutic treatments and potential applications in human bodies. Thus, the main focus of this review is to highlight the most recent progress on the design of various controlled MSN gatekeepers to achieve 'zero premature release' drug delivery. The diverse gatekeepers are categorised into the following kinds according to their types and characteristics: (1) polymers; (2) inorganic nanomaterials; (3) host-guest assemblies; and (4) biomacromolecules. This review will offer a broad palette of opportunities for researchers with interests including nanomaterial fabrication and modification, targeted drug delivery and stimuli-responsive drug release.

Hydrogen sulfide (H2S) is emerging as an important gasotransmitter but remains difficult to study. Here we report a novel two-photon fluorescent probe with NIR emission for H2S detection. It was successfully used to realize H2S imaging in bovine serum, living cells, tissues as well as in living mice.

Condensation of 2-(2'-aminophenyl)benzoxazole with p-toluenesulfonyl chloride and phenyl isocyanate yields two new anion sensors (TABO and PUBO), which can undergo excited-state intramolecular proton transfer (ESIPT) upon excitation. For the acid receptor TABO, the ESIPT process can be readily disturbed by basic anions such as F-, CH3COO-, and H2PO4- by deprotonating the sulfonamide unit, whereas in the case of PUBO, a good hydrogen-bonding donor, the ESIPT process is inhibited either by the fluoride-induced deprotonation of the urea unit or by the formation of a strong CH3COO--urea intermolecular hydrogen bond complex, and these two types of inhibition mechanisms consequently result in different ratiometric responses. But other anions with less hydrogen-bonding acceptor abilities cannot inhibit the ESIPT. Interestingly, the different inhibition abilities of F-, CH3COO-, and H2PO4- produce different spectral behaviors in PUBO, so this new sensor successfully distinguishes the subtle difference in these three anionic substrates of similar basicity and surface charge density.

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Carbon-based nanomaterials as important agents for biological applications have emerged in the past few years due to their unique optical, electronic, mechanical, and chemical properties. Many of these applications rely on successful surface modifications. This review article comprises two main parts. In the first part, we briefly review the properties and surface modifications of several classes of carbon nanomaterials, mainly carbon nanotubes (CNTs), graphene and its derivatives, carbon dots (CDs) and graphene quantum dots (GQDs), as well as some other forms of carbon-based nanomaterials such as fullerene, carbon nanohorns (CNHs) and carbon nanoonions (CNOs). In the second part, we focus on the biological applications of these carbon nanomaterials, in particular their applications for fluorescence biosensing as well as bioimaging.