Anal. Chem. 2004, 76, 458-463
Technical Notes
Analysis in Ultrasmall Volumes: Microdispensing of Picoliter Droplets and Analysis without Protection from Evaporation Sebastian Neugebauer,† Stephanie R. Evans,‡ Zoraida P. Aguilar,‡ Marcus Mosbach,† Ingrid Fritsch,*,‡ and Wolfgang Schuhmann*,†
Analytische Chemie, Elektroanalytik & Sensorik, Ruhr-Universita¨t Bochum, Universita¨tsstrasse 150, D-44780 Bochum, Germany, and Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas 72701
A new approach is reported for analysis of ultrasmall volumes. It takes advantage of the versatile positioning of a dispenser to shoot ∼150-pL droplets of liquid onto a specific location of a substrate where analysis is performed rapidly, in a fraction of the time that it takes for the droplet to evaporate. In this report, the site where the liquid is dispensed carries out fast-scan cyclic voltammetry (FSCV), although the detection method does not need to be restricted to electrochemistry. The FSCV is performed at a microcavity having individually addressable gold electrodes, where one serves as working electrode and another as counter/pseudoreference electrode. Five or six droplets of 10 mM [Ru(NH3)6]Cl3 in 0.1 M KCl were dispensed and allowed to dry, followed by redissolution of the redox species and electrolyte with one or five droplets of water and immediate FSCV, demonstrating the ability to easily concentrate a sample and the reproducibility of redissolution, respectively. Because this approach does not integrate detection with microfluidics on the same chip, it simplifies fabrication of devices for analysis of ultrasmall volumes. It may be useful for singlestep and multistep sample preparation, analyses, and bioassays in microarray formats if dispensing and changing of solutions are automated. However, care must be taken to avoid factors that affect the aim of the dispenser, such as drafts and clogging of the nozzle.
Self-contained fast-scan cyclic voltammetry (FSCV) at microelectrochemical cavities was achieved on volumes of ∼150-750 pL that were delivered from a microdispenser. This is the first report of an approach to analyze ultrasmall volumes (
