Design and synthesis of novel palladium cyclometallate-based fluorescent probe: Studies on interaction with cell membrane by confocal and fluorescence lifetime imaging.

Coordination complexes offer great potential as cellular imaging probes, which allow to examine specific cell organelle structures in their physiological conditions to better understand the biological system. Understanding the heterogeneous nature of the cell membrane could unveil details of their functionality. Here, we have developed a new anthracene conjugated fluorescent palladium(II) cyclometallate [PdL1Cl] where L1H = [2-(2- (anthracen-9-ylmethylene)-1-phenylhydrazineyl)pyridine] (H stands for dissociable proton), which not only specifically stains the cell membrane, but could be utilized to visualise the membrane by the confocal and fluorescence lifetime imaging microscopy (FLIM). This probe is unable to enter inside the cell as it did not pass through the cell membrane via diffusion or various organic and metal transporters. However, the great lipophilicity of fluorescein improves the interaction of the probe with the peptidoglycan layer of the cell membrane. Probable dissociation of chloride ion and formation of positively charged palladium complex resulted in staining the negatively charged cell membrane. The 3D confocal imaging clearly expressed sole membrane staining by the probe. The probe efficiently stains both cancer cells (HeLa and MCF-7 cell lines) and normal cell (HEK 293 T), confirming the universality of the probe in membrane staining.

Super-Resolution Microscopy Revealed the Lysosomal Expansion During Epigallocatechin Gallate-Mediated Apoptosis.

Direct visualization of the dynamic events in lysosomes during drug-mediated programmed cell death (apoptosis) is a great challenge. This is due to the lack of resolving power of a conventional microscope and also the unavailability of a suitable multimodal probe that simultaneously can carry the drug with high loading capacity and ensure its specific internalization into lysosomes. In this work, using super-resolution microscopy, we observed the lysosomal expansion during apoptosis that was treated with epigallocatechin gallate (EGCG) conjugated to bovine serum albumin (BSA). Albumin protein is known to internalize into lysosomes via endocytosis, thus helping in the specific delivery of EGCG to the lysosomal compartment. The conjugation of EGCG to BSA not only helped in increasing the killing efficiency of cancer cells but it also reduces the side effects and produces minimal reactive oxygen species. The decrease in local viscosity helped in lysosomal expansion during apoptosis.

Bovine Serum Albumin-Conjugated Red Emissive Gold Nanocluster as a Fluorescent Nanoprobe for Super-resolution Microscopy.

The gold nanocluster (GNC), because of its interesting photoluminescence properties and easy renal clearance from the body, has tremendous biomedical applications. Unfortunately, it has never been explored for super-resolution microscopy (SRM). Here, we present a protein-conjugated red emissive GNC for super-resolution radial fluctuation (SRRF) of the lysosome in HeLa cells. The diameter of the lysosome obtained in SRRF is ∼59 nm, which is very close to the original diameter of the smallest lysosome in HeLa cells. Conjugation of protein to GNC aided in the specific labeling of the lysosome. We hope that GNC not only will replace some of the common dyes used in SRM but due to its electron beam contrast could also be used as a multimodal probe for several other correlative bioimaging techniques.