Enhanced biosensing of tumor necrosis factor-alpha based on aptamer-functionalized surface plasmon resonance substrate and Goos-Hänchen shift.

Tumor necrosis factor-alpha (TNF-α) serves as a crucial biomarker in various diseases, necessitating sensitive detection methodologies. This study introduces an innovative approach utilizing an aptamer-functionalized surface plasmon resonance (SPR) substrate together with an ultrasensitive measure, the Goos-Hänchen (GH) shift, to achieve sensitive detection of TNF-α. The developed GH-aptasensing platform has shown a commendable figure-of-merit of 1.

Label-free biosensing with singular-phase-enhanced lateral position shift based on atomically thin plasmonic nanomaterials.

Rapid plasmonic biosensing has attracted wide attention in early disease diagnosis and molecular biology research. However, it was still challenging for conventional angle-interrogating plasmonic sensors to obtain higher sensitivity without secondary amplifying labels such as plasmonic nanoparticles. To address this issue, we developed a plasmonic biosensor based on the enhanced lateral position shift by phase singularity.

Advanced quantification for single-cell adhesion by variable-angle TIRF nanoscopy.

Over the last decades, several techniques have been developed to study cell adhesion; however, they present significant shortcomings. Such techniques mostly focus on strong adhesion related to specific protein-protein associations, such as ligand-receptor binding in focal adhesions. Therefore, weak adhesion, related to less specific or nonspecific cell-substrate interactions, are rarely addressed.

Evaluation of diffusion coefficient of P-glycoprotein molecules labeled with green fluorescent protein in living cell membrane.

The movement of individual molecules inside living cells has recently been resolved by single particles tracking (SPT) method which is a powerful tool for probing the organization and dynamics of the plasma membrane constituents. Effective treatment of metastatic cancers requires the toxic chemotherapy, however this therapy leads to the multidrug resistance phenomenon of the cancer cells, in which the cancer cells resist simultaneously to different drugs with different targets and chemical structures. P-glycoprotein molecules which are responsible for multidrug resistance of many cancer cells have been studied by cancer biologists during past haft of century.

Incidence angle calibration for prismless total internal reflection fluorescence microscopy.

We propose a calibration routine useful to evaluate the incident angle in total internal reflection fluorescence (TIRF) microscopy. This procedure is based on critical angle measurements conducted in the back focal plane (BFP) of the objective. Such BFP imaging can be easily implemented on any TIRF setup, making this technique very attractive.

Topography of Cells Revealed by Variable-Angle Total Internal Reflection Fluorescence Microscopy.

We propose an improved version of variable-angle total internal reflection fluorescence microscopy (vaTIRFM) adapted to modern TIRF setup. This technique involves the recording of a stack of TIRF images, by gradually increasing the incident angle of the light beam on the sample. A comprehensive theory was developed to extract the membrane/substrate separation distance from fluorescently labeled cell membranes.

Nanoscale characterization of vesicle adhesion by normalized total internal reflection fluorescence microscopy.

We recently proposed a straightforward fluorescence microscopy technique to study adhesion of Giant Unilamellar Vesicles. This technique is based on dual observations which combine epi-fluorescence microscopy and total internal reflection fluorescence (TIRF) microscopy: TIRF images are normalized by epi-fluorescence ones. By this way, it is possible to map the membrane/substrate separation distance with a nanometric resolution, typically ~20 nm, with a maximal working range of 300-400 nm.

Axial nanoscale localization by normalized total internal reflection fluorescence microscopy.

We present a simple modification of a standard total internal reflection fluorescence microscope to achieve nanometric axial resolution, typically ≈10  nm. The technique is based on a normalization of total internal reflection images by conventional epi-illumination images. We demonstrate the potential of our method to study the adhesion of phopholipid giant unilamellar vesicles.

Multiphoton cascade absorption in single molecule fluorescence saturation spectroscopy.

Saturation spectroscopy is a relevant method to investigate photophysical parameters of single fluorescent molecules. Nevertheless, the impact of a gradual increase, over a broad range, of the laser excitation on the intramolecular dynamics is not completely understood, particularly concerning their fluorescence emission (the so-called brightness). Thus, we propose a comprehensive theoretical and experimental study to interpret the unexpected evolution of the brightness with the laser power taking into account the cascade absorption of two and three photons.

Microfluidity mapping using fluorescence correlation spectroscopy: a new way to investigate plasma membrane microorganization of living cells.

Diffusion time distribution analysis has been employed to highlight the microfluidity fingerprint of plasma membrane of living cells. Diffusion time measurements were obtained through fluorescence correlation spectroscopy performed at the single cell level, over various eukaryotic cell lines (MCF7, LR73, KB3.1, MESSA and MDCKII).

Enhancement and quenching regimes in metal-semiconductor hybrid optical nanosources.

We report on the emission of hybrid nanosources composed of gold nanoparticles coupled with quantum dots. The emission relies on energy transfer from the quantum dots to gold nanoparticles which could be de-excited through radiative plasmon relaxation. The dependence of the emission efficiency is studied systematically as a function of the size of gold nanoparticles and interdistance between gold nanoparticles and quantum dots.

High heterogeneity of plasma membrane microfluidity in multidrug-resistant cancer cells.

Diffusion-time distribution analysis (DDA) has been used to explore the plasma membrane fluidity of multidrug-resistant cancer cells (LR73 carcinoma cells) and also to characterize the influence of various membrane agents present in the extracellular medium. DDA is a recent single-molecule technique, based on fluorescence correlation spectroscopy (FCS), well suited to retrieve local organization of cell membrane. The method was conducted on a large number of living cells, which enabled us to get a detailed overview of plasma membrane microviscosity, and plasma membrane micro-organization, between the cells of the same line.

Surface modified single molecules free-diffusion evidenced by fluorescence correlation spectroscopy.

We report on the free diffusion of single molecule near an interface studied using fluorescence correlation spectroscopy. In particular, we show that the chemical nature of the substrate may modify the free diffusion of a widely used molecule (rhodamine 6G), thus inducing unexpected effects in fluorescence correlation spectroscopy measurements. Our results show a strong influence, up to a few micrometer from the interface, of the surface polarity.

Spatial fluorescence cross-correlation spectroscopy.

We present an alternative method for diffusion measurements of fluorescent species in solution by use of confocal microscopy and fluorescence correlation spectroscopy techniques. It consists of making a time and spatial dual correlation in which one detects the fluorescence signals from two nearby separate confocal volumes and cross correlates them. To improve the spatial discrimination between the two confocal volumes we propose filtering of fluorescence photocounts by rejecting the fluorescence background, which corresponds to particles located far from the center of the detection volumes.