Sub-Attomole Molecule Detection in a Single Biological Cell in-vitro by Thermal Lens Microscopy

We have developed a novel thermal lens microscopy coupled with an optical microscope, and presently applied it to the ultratrace molecule detection in a single biological cell (mouse hybridoma) in-vitro. The determination results obtained for individual cells were calibrated by the average values determined by absorption spectrophotometry. The determination limit of the thermal lens microscope, defined as twice the standard deviation of the calibration curve, was 37.8 amol/cell, which was more than one order smaller than that of a fluorescence microscope under our experimental conditions. This superiority should come from escaping light scattering by a cell membrane and by cytoplasm, which is inevitable in fluorescence spectrometry. The absolute determination limit of the thermal lens microscopy was calculated down to sub-attomole level. In addition, the method is more widely applicable, even to non-fluorescent samples without chemical preparation, and therefore, the thermal lens microscope has proved to be very useful in directly quantifying ultratrace chemical species in a single biological cell in-vitro.