A novel connected-groove micromixer (CGM) has been designed, fabricated, and investigated thoroughly. Connected grooves in this device, crossing multiple sides of the microchannel induced an intensely transverse field of fluids, and thus generating rapid mixing than patterned grooves on a single side alone. The fabrication of a CGM was facilitated to overcome the complication of fabricating the sidewall and bottom grooves in a channel simultaneously; a CGM hence became highly efficient and compact. We propose here CGM of two types-CGM-1 and CGM-2-and compare their mixing performance with a slanted-groove micromixer (SGM) numerically and experimentally for Re over a wide range (1-100). Numerical analysis demonstrated that a CGM provided intense transverse components in the field and great mixing efficiency; in particular, CGM-2 with co-rotating flows encompassing the mechanisms of cutting and blending of fluids had a mixing performance over 50% better than an SGM for Re = 1-100. To systematically analyze the mixing by experiments, mixing of slightly viscous fluids, highly viscous fluids, and bio-fluids were adopted, respectively. The mixing experiments of stightly viscous dye solutions on the basis of the color uniformity of mixture showed that mixing lengths of both CGM were smaller than that of SGM. Based on the mixing results of highly viscous fluids, CGM-1 with sidewall grooves had a shorter pitch of spiral flow and more helical turns than an SGM. With a confocal microscope we explored the mixing sections of fluorescent proteins (B-phycoerythrin, BPE; Allophycocyanin alpha subunit, ApcA) inside a micronfixer to confirm the numerical results. (C) 2007 Elsevier Ltd. All rights reserved.