Airborne cell analysis

A miniaturized analysis system for the study of living cells and biochemica l reactions in microdroplets was developed. The technique utilizes an in-ho use-developed piezoelectric now-through droplet dispenser for precise reage nt supply and an ultrasonic levitator for contactless sample handling. A fe w-cell study was performed with living primary adipocytes. Droplets (500 nL ) containing 3-15 individual cells were acoustically levitated. The additio n of beta-adrenergic agonists into the levitated droplet using the droplet dispenser stimulated adipocyte lipolysis, leading to free fatty acid releas e and a consequent pH decrease of the surrounding buffer. The addition of i nsulin antagonized lipolysis and hence also the decrease in pH, The changes in pH, i.e., the cell response in the droplet, were followed using a pH-de pendent fluorophore continuously monitored by fluorescence imaging detectio n. An image analysis computer program was employed to calculate the droplet intensities. To counteract droplet evaporation, found to affect the fluore scence intensities, a separate dispenser was used to continually add water, thus keeping the droplet volume constant.