Biomedical subjects

Sudipta Maiti

Publications and source records attributed to Sudipta Maiti.

5 recordsLinked to original sources

PubMed2006

Fiber-optic fluorescence correlation spectrometer.

Fluorescence correlation spectroscopy (FCS) is a sensitive technique used to probe size, concentration, flow velocity, and reaction kinetics in a dilute solution. Conventional FCS spectrometers achieve this sensitivity at the cost of using bulky optics. We demonstrate a technique that utilizes a single-mode optical fiber of 3.3 microm mode field diameter to perform FCS measurements. We demonstrate that the technique has adequate sensitivity to perform FCS measurements on fluorescent beads of 13 nm radius, and that the results agree with theoretical predictions. Our method potentially allows FCS to be extended to remote and in vivo applications.

Colloids↗

PubMed2005

Fluorescence correlation microscopy with real-time alignment readout.

In confocal fluorescence correlation microscopy (FCM) it is important to ensure that the correlation measurement is actually performed at the chosen location of the three-dimensional image of the specimen. We present a confocal FCM design that provides an automatic real-time readout of the location in the confocal microscopic image, which is aligned with the detector of the fluorescence correlation spectrometer. The design accomplishes this without using any special positioning device. The design is based on an apertured fluorescence detector placed close to the back aperture of the objective lens and can be easily incorporated into virtually any confocal microscope. We demonstrate the method by performing FCM measurements of a dye diffusing on a cell membrane.

Calibration↗

PubMed2004

Microfluorometric detection of catecholamines with multiphoton-excited fluorescence.

We demonstrate sensitive spatially resolved detection of physiological chromophores that emit in the ultraviolet (<330 nm). An atypical laser source (a visible wavelength femtosecond optical parametric oscillator), and an unconventional collection geometry (a lensless detector that detects the forward-emitted fluorescence) enable this detection. We report the excitation spectra of the catecholamines dopamine and norepinephrine, together with near-UV emitters serotonin and tryptophan, in the range of 550-595 nm. We estimate the molecular two-photon action cross section of dopamine, norepinephrine, and serotonin to be 1.2 mGM (1 GM, or Goppert Mayor, is equal to 10(-58) m4 s(-1) photon(-1)), 2 mGM, and 43 mGM, respectively, at 560 nm. The sensitivity achieved by this method holds promise for the microscopic imaging of vesicular catecholamines in live cells.

Catecholamines↗

PubMed2003

Axial resolution limit of a fiber-optic fluorescence probe.

We examine the limit of spatial resolution achievable when a sine optical fiber is used for excitation and collection of fluorescence from a bulk specimen. We calculate the probability of detecting a fluorescent particle as a function of its position relative to the fiber face, using excitation wavelength lambda, radius a, numerical aperture N.A., and the particle's fluorescence and absorbance spectra. Treating Rhodamine B as a model fluorescent analyte and using appropriate fiber parameters, we show that the maximum axial resolution (defined as the axial distance in a homogenous solution within which 50% of the detected signal originates) achievable is approximately 10 microm. We experimentally measured the axial resolution for a 500-microM aqueous solution of Rhodamine B with lambda = 543 nm, a = 1.31 microm, and a N.A. of 0.16 and found good qualitative agreement with the calculation.

Journal Article↗

PubMed2002

Measuring diffusion in cell membranes by fluorescence correlation spectroscopy.

Fluorescence Correlation Spectroscopy (FCS) can measure diffusion on the cell surface with unparalleled sensitivity. In appropriate situations, this can be the most sensitive and accurate method for measuring receptor interaction and oligomerization. Here we attempt to describe FCS in sufficient detail so that the reader is able to judge when there is a compelling reason to choose this technique, understand the basic theory behind it, construct a FCS spectrometer in the laboratory, and analyze the data to obtain a meaningful estimate of the physical parameters.

Artifacts↗