A new molecular dyad consisting of a Cy5 chromophore and ferrocene (Fc) and a triad consisting of Cy5, Fc, and β-cyclodextrin (CD) are synthesized and their photophysical properties investigated at both the ensemble and single-molecule levels. Hole transfer efficiency from Cy5 to Fc in the dyad is reduced upon addition of CD. This is due to an increase in the Cy5-Fc separation (r) when the Fc is encapsulated in the macrocyclic host. On the other hand, the triad adopts either a Fc-CD inclusion complex conformation in which hole transfer quenching of the Cy5 by Fc is minimal or a quasi-static conformation with short r and rapid charge transfer. Single-molecule fluorescence measurements reveal that r is lengthened when the triad molecules are deposited on a glass substrate. By combining intramolecular charge transfer and competitive supramolecular interaction, the triad acts as an efficient chemical sensor to detect different bioactive analytes such as amantadine hydrochloride and sodium lithocholate in aqueous solution and synthetic urine.

Here, a set of novel and personalized nanocarriers are presented for controlled nucleus-targeted antitumor drug delivery and real-time imaging of intracellular drug molecule trafficking by integrating an enzyme activatable cell penetrating peptide (CPP) with mesoporous silica coated quantum dots nanoparticles. Upon loading of antitumor drug, doxorubicin (DOX) and further exposure to proteases in tumor cell environment, the enzymatic cleavage of peptide sequence activates oligocationic TAT residues on the QDs@mSiO2 surface and direct the DOX delivery into cellular nucleus. The systematic cell imaging and cytotoxicity studies confirm that the enzyme responsive DOX-loaded CPP-QDs@mSiO2 nanoparticles can selectively release DOX in the tumor cells with high cathepsin B enzyme expression and greatly facilitate DOX accumulation in targeted nucleus, thus exhibiting enhanced antitumor activity in these cells. As contrast, there is limited nuclear-targeted drug accumulation and lower tumor cytotoxicity observed in the cells without enzyme expression. More importantly, significant antitumor DOX accumulation and higher tumor inactivation is also found in the drug resistant tumor cells with targeted enzyme expression. Such simple and specific enzyme responsive mesoporous silica-QDs nanoconjugates provide great promise for rational design of targeted drug delivery into biological system, and may thus greatly facilitate the medical theranostics in the near future.

Real-time imaging of cell-surface-associated proteolytic enzymes is critical to better understand their performances in both physiological and pathological processes. However, most current approaches are limited by their complexity and poor membrane-anchoring properties. Herein, we have designed and synthesized a unique small-molecule fluorescent probe, which combines the principles of passive exogenous membrane insertion and Förster resonance energy transfer (FRET) to image cell-surface-localized furin-like convertase activities. The membrane-associated furin-like enzymatic cleavage of the peptide probe leads to an increased fluorescence intensity which was mainly localized on the plasma membrane of the furin-expressed cells. This small-molecule fluorescent probe may serve as a unique and reliable reporter for real-time visualization of endogenous cell-surfaceassociated proteolytic furin-like enzyme functions in live cells and tissues using one-photon and two-photon microscopy.

Bacterial resistance to antibiotics poses a great clinical challenge in fighting serious infectious diseases due to complicated resistant mechanisms and time-consuming testing methods. Chemical reaction-directed covalent labeling of resistance-associated bacterial proteins in the context of a complicated environment offers great opportunity for the in-depth understanding of the biological basis conferring drug resistance, and for the development of effective diagnostic approaches. In the present study, three fluorogenic reagents LRBL1–3 for resistant bacteria labeling have been designed and prepared on the basis of fluorescence resonance energy transfer (FRET). The hydrolyzed probes could act as reactive electrophiles to attach the enzyme, β-lactamase, and thus facilitated the covalent labeling of drug resistant bacterial strains. SDS electrophoresis and MALDI-TOF mass spectrometry characterization confirmed that these probes were sensitive and specific to β-lactamase and could therefore serve for covalent and localized fluorescence labeling of the enzyme structure. Moreover, this β-lactamase-induced covalent labeling provides quantitative analysis of the resistant bacterial population (down to 5 %) by high resolution flow cytometry, and allows single-cell detection and direct observation of bacterial enzyme activity in resistant pathogenic species. This approach offers great promise for clinical investigations and microbiological research.

Surface-enhanced Raman scattering (SERS) spectroscopy and density functional theory (DFT) calculations were used to investigate the nature of the charge-transfer (CT) process between nitrothiophenol (NTP) isomers and the n-type semiconductor, TiO₂. The Raman signals of p-NTP and m-NTP that were chemisorbed onto TiO₂ were significantly enhanced with respect to their corresponding neat compounds. In particular, an enhancement factor (EF) of 10²–10³ was observed for both p-NTP and m-NTP, with m-NTP displaying a larger EF compared to p-NTP. The Raman signal of o-NTP on TiO₂ was not detectable, owing to interference from fluorescence emissions. A molecule-to-TiO₂ charge-transfer mechanism was responsible for the enhanced Raman signals observed in p-NTP and m-NTP. This transfer was due to a strong coupling between the adsorbate and the metal oxide, which led to an optically driven CT transition from the HOMO of NTP into the conduction band of TiO₂. Based on the mesomeric effect, the NO₂ group para to the thiol had a stronger electron-withdrawing ability than the NO₂ group at the meta position. A less-efficient CT transition from p-NTP to TiO₂ in the surface complex resulted in a weaker Raman-signal enhancement for p-NTP compared to m-NTP. The DFT calculation determined that the HOMO and the LUMO of NTP bound to TiO₂ were located entirely on the adsorbate and the semiconductor, respectively, thereby supporting the experimental findings that a molecule-to-TiO₂ mechanism was the driving force behind the observed SERS effect.

The molecular interactions of the glycopeptide antibiotic vancomycin (Van) with bacterial cell wall analogues N,N′-diacetyl-L-Lys-D-Ala-D-Ala (Ac₂KdAdA) and N,N′-diacetyl-L-Lys-D-Ala-D-Lac (Ac₂KdAdL) were investigated in neat water, phosphate buffer and HEPES buffer by using fluorescence correlation spectroscopy (FCS) and molecular dynamics (MD) simulations. The FCS determined dissociation constants (k_d) show that the intrinsic binding affinity between Van and the drug-sensitive peptide ligand Ac₂KdAdA remains invariant when the solvent is changed from neat water to either PBS or HEPES buffer; this demonstrates that there are no obvious solvent effects on the association between Van and Ac₂KdAdA due to the strong intermolecular interaction between the two moieties. When compared to Ac₂KdAdA, a significantly larger k_d value was observed for the binding between the drug-resistant peptide ligand Ac₂KdAdL and Van. Furthermore, the k_d increased by about 8- to 11-times when the solvent was changed from neat water to 10 mM phosphate/HEPES buffer. The stability of the Ac₂KdAdL–Van complex was dependent on the concentration of the buffer and k_d increases as the concentration of either phosphate ions or HEPES increased until an equilibrium was attained. Both FCS and MD simulation studies clearly showed that the components constituting the buffer solution (e.g., phosphate ions and HEPES) are involved in molecular interactions with the binding pocket of Van and they profoundly affect the intrinsic stability of the complex formed between the low-affinity Ac₂KdAdL and Van. These results could help us to better understand the detailed structure and activity of glycopeptide antibiotic derivatives toward bacterial cell wall peptide analogues, and can further facilitate the development of new drug candidates against drug-resistant bacterial strains.