Noninvasive metabolic assessment of single cells

Because metabolism is fundamental to the successful functioning of a cell, perturbations in metabolism can signal compromised viability. For the assessment of viability, analyses not only must be sensitive enough to be employed at the single cell level, but also noninvasive. Ultramicrofluorescence is a technique that fulfills both criteria. By using specially prepared constriction pipets, created on a microforge and calibrated with tritiated water, volumes in the nanoand picoliter range can be accurately delivered. A miniaturization of enzymatic analysis using a fluorescence microscope, with either photometer or charge-coupled device attachments, is then employed to quantitate biochemical reactions in such submicroliter volumes. Subsequently, samples of culture medium surrounding an individual cell can be taken and analyzed in order to determine the rate of utilization or production of various metabolites in real time.