Approaches to increasing surface stress for improving signal-to-noise ratio of microcantilever sensors

Abstract

Microcantilever sensor technology has been steadily growing for the last 15 years. While we have gained a great amount of knowledge in microcantilever bending due to surface stress changes, which is a unique property of microcantilever sensors, we are still in the early stages of understanding the fundamental surface chemistries of surface-stress-based microcantilever sensors. In general, increasing surface stress, which is caused by interactions on the microcantilever surfaces, would improve the S/N ratio and subsequently the sensitivity and reliability of microcantilever sensors. In this review, we will summarize (A) the conditions under which a large surface stress can readily be attained and (B) the strategies to increase surface stress in case a large surface stress cannot readily be reached. We will also discuss our perspectives on microcantilever sensors based on surface stress changes.

Figure 1

Scheme (left, Veeco Instruments, Santa Barbara, CA) and Electron micrograph (right, fabricated in our lab) of cantilevers. The sizes of the cantilevers on the right vary from 5 μm to 200 μm in length, extending from the support.

Figure 2

Two mechanisms of binding-induced surface stress on different types of responsive coatings. Left: tensile stresses for antigen-antibody interaction; right: compressive stress due to neutralization of excessive charge on the surface.

Figure 3

(a) Top view of the system. A schematic representation of the front of the cell is shown in (b). Reprinted with permission from the Elsevier B.V.

Figure 4

LbL nanoassembly with intercalated enzyme on the MCL surface. Reprinted with permission from the American Chemical Society.

Figure 5

Bending of single-side brush-modified cantilever with changing pH and schematic illustration of brush conformation in different regimes. Reprinted with permission from the American Chemical Society.

Figure 6

Deflection, Δz, and changes in surface stress, Δσ, of the sensors are plotted as a function of time for exposure to alkanethiol and a reference vapor. Reprinted with permission from the American Association for the Advancement of Science.

Figure 7

STM images (3 μm × 3 μm) of (A) large-grained gold and (B) small-grained gold. Reprinted with permission from the American Chemical Society.

Figure 8

Atomic force microscopy topography images (0.5 × 0.5 μm²) of 60 nm thick gold films deposited on the silicon cantilevers at (a) 0.02 nm/s, (b) 0.2 nm/s, and (c) 0.3 nm/s. Reprinted with permission from the American Institute of Physics.