Tailoring the Sensitivity of Microcantilevers To Monitor the Mass of Single Adherent Living Cells

Abstract

Microcantilevers are widely employed as mass sensors for biological samples, from single molecules to single cells. However, the accurate mass quantification of living adherent cells is impaired by the microcantilever's mass sensitivity and cell migration, both of which can lead to detect masses mismatching by ≫50%. Here, we design photothermally actuated microcantilevers to optimize the accuracy of cell mass measurements. By reducing the inertial mass of the microcantilever using a focused ion beam, we considerably increase its mass sensitivity, which is validated by finite element analysis and experimentally by gelatin microbeads. The improved microcantilevers allow us to instantly monitor at much improved accuracy the mass of both living HeLa cells and mouse fibroblasts adhering to different substrates. Finally, we show that the improved cantilever design favorably restricts cell migration and thus reduces the large measurement errors associated with this effect.

Monitoring the mass, eigenfrequency, and quality factor of mammalian cells

“…Recently, we introduced shorter microcantilevers to reduce their inertial mass and thus to increase the sensitivity (e.g., mass resolution) at which the total cell mass can be measured 29 , 30 . More advanced designs that cut out rectangular sections of the microcantilever beam allow to considerable reduce the cantilever mass without the need of shortening the microcantilever, to reduce the laser intensity needed for photothermal actuation of the microcantilever and thus possible effects of phototoxicity, and, importantly, to restrict cell migration in order to minimize measurement errors associated with the cell changing its position along the microcantilever 30 .…”

“…To account for the position of the cell along the beam of the microcantilever, is multiplied by a correction factor to receive the total cell mass (Supplementary Note 1 ) 27 . Recently introduced designs that reduce the mass of the microcantilever enable to monitor the mass of single adherent cells at much-improved accuracy and higher mass sensitivity 29 , 30 . However, the equation simplifies the cell as a solid mass, while living cells dynamically change shape, adhesion, spreading, and mechanics (e.g., cortex tension, pressure, and stiffness) during the cell cycle 31 – 34 .…”

Optical Nanofiber-Enabled Self-Detection Picobalance

“…Developing ultrasensitive force (or masses) sensors capable of measuring force down to the piconewton level is of fundamental importance for a wide range of disciplines, including molecular biology, − cell biology, − micromanipulation, , and fundamental physics . For example, the mass fluctuations of cells, single-virus force spectroscopy, and optical forces can be precisely measured by specially designed microelectromechanical systems (MEMS) force sensors or advanced instruments (e.g., atomic force microscopy (AFM)).…”

Modeling Nonlinear Dynamics of Functionalization Layers: Enhancing Gas Sensor Sensitivity for Piezoelectrically Driven Microcantilever

“…12 This study focuses on using the dynamic method to quantify the amount of cadaverine measured by changes in resonance frequency. The variation of resonance frequency with mass added can be summarized by eq 1 15 = i k j j j j j j y…”

“…This study focuses on using the dynamic method to quantify the amount of cadaverine measured by changes in resonance frequency. The variation of resonance frequency with mass added can be summarized by eq δ m = k e q 4 π 2 true( 1 ( f r − δ f r ) 2 − 1 f normalr 2 true) where f r (Hz) is the measured resonance frequency, δ f r (Hz) is the measured change in resonance frequency, k eq is the lumped spring constant of the microcantilever system, and δ m (μg) is the adsorbed mass in this case. Usually, the functionalization layer of the microcantilever is thin and is assumed to have a negligible effect on the overall stiffness of the system, with k being constant.…”