This paper presents the design, analysis, fabrication, and characterization of an electrostatically driven single-axis active probing device for the applications of cellular force sensing and materials characterization. The active microprobe is actuated by linear comb drivers to generate the motion in the probing direction. Both actuation and sensing comb-drive structures are designed for the probing stage. The sensing comb structures enable us to sense the probe displacement when the device is actuated, which enables applications of force-balanced sensing and provides the capability of closed-loop control towards better accuracy. The designed active probing device is fabricated on a silicon-on-insulator (SOI) substrate with a 10？μm thick device layer through surface micromachining technologies and deep reactive-ion etching (DRIE) process. The handle layer beneath probe stage is etched away by DRIE process to decrease the film damping between the stage and the handle wafer thus achieving high-quality factor. The fabricated stage provides a motion range of 14？μm at actuation voltage of 140？V. The measured natural frequency of the stage is 1.5？kHz under ambient conditions. A sensitivity of 6？fF/μm has been achieved. The proposed single-axis probe is aimed at sensing cellular force which ranges from a few nano-Newton to μN and micromanipulation applications. 1. Introduction Different from many engineering materials, living cells exhibit much more complex functions by sensing external stimuli, such as mechanical force, electrical field, chemical and density gradient, and converting them into biological reactions. Research on mechanics of cells has attracted much attention and progressed very fast during past decade for the reason that mechanical loading of cells in forms of deformation and remodelling is known to have significant impact on disease detection and human health [1]. Moreover, study of mechanics in cells and subcellular component is critical for understanding the interaction between mechanical signals and biological behaviours such as cell growth, proliferation, and differentiation. Since cellular and subcellular forces usually range from sub-nN (10？9？N) to μN (10？6？N) [2], high force sensitivity and high positioning resolution are generally required for cell manipulators and cellular force sensors. Conventional techniques for sensing and manipulating cells include atomic force microscopy (AFM) [3], magnetic twisting cytometry (MTC) [4], piezoresistive and piezoelectric force sensor [5, 6], and capacitive cellular force sensor using transverse
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