Serial weighting of micro-objects with resonant microchanneled cantilevers

Abstract

Atomic force microscopy (AFM) cantilevers have proven to be very effective mass sensors. The attachment of a small mass to a vibrating cantilever produces a resonance frequency shift that can be monitored, providing the ability to measure mass changes down to a few molecules resolution. Nevertheless, the lack of a practical method to handle the catch and release process required for dynamic weighting of microobjects strongly hindered the application of the technology beyond proof of concept measurements. Here, a method is proposed in which FluidFM hollow cantilevers are exploited to overcome the standard limitations of AFM-based mass sensors, providing high throughput single object weighting with picogram accuracy. The extension of the dynamic models of AFM cantilevers to hollow cantilevers was discussed and the effectiveness of mass weighting in air was validated on test samples.

Elasticity Spectra as a Tool to Investigate Actin Cortex Mechanics

“…The spring constant was determined in air by thermal tuning and the Sader's method [77] and the channel was filled with physiological solution containing 0.1 mg/ml of the blue fluorescent dye AMCA (7-amino-4-methylcoumarin, Sigma-Aldrich, USA) for blockage detection. Green fluorescent beads (Phosphorex Inc, USA) with 3µm to 4µm diameter were placed next to the confluent cell layer and attached to the cantilever tip by applying 800mbar suction pressure through the microchannel [71,78]. Indentations were performed at 1µm/s approach speed and up to 100nN force setpoint in grids of 5x5 points with 25µm pitch.…”

Elasticity Spectra as a Tool to Investigate Actin Cortex Mechanics

“…The spring constant was determined in air by thermal tuning and the Sader's method [82] and the channel was filled with physiological solution containing 0.1 mg/ml of the blue fluorescent dye AMCA (7-amino-4-methylcoumarin, Sigma-Aldrich, USA) for blockage detection. Green fluorescent beads (Phosphorex Inc, USA) with 3µm to 4µm diameter were placed next to the confluent cell layer and attached to the cantilever tip by applying 800mbar suction pressure through the microchannel [74,83]. Indentations were performed at 1µm/s approach speed and up to 100nN force setpoint in grids of 5x5 points with 25µm pitch.…”

A Versatile Mass-Sensing Platform With Tunable Nonlinear Self-Excited Microcantilevers

“…The position of the bead along the major axis of the cantilever changes its resonance frequency and, therefore, the added mass calculated with (5). References [12] and [41] discuss a method to correct for this effect, based in shape of the vibrating mode. In the experiments described here, the error between values of mass added to the cantilever obtained using both methods was found to be within the experimental error of the setup and therefore this correction was discarded for the sake of simplicity.…”

“…where ( ) = ( ) ( ) − . Equation (11) shows that the overall loop gain must be unitary, while (12) states that the total phase shift around the loop must be an integer multiple of 2π radians. By decomposing the total phase of the transfer function ( ) and using (9), equation (12) can be rewritten as:…”

“…In addition, when individual masses, such as cells or proteins, are attached, the response of the resonator depends on the actual position of the added mass [11]. Therefore, negative pressure in hollow cantilevers [12], mechanical traps [13] or centrifugal forces [14] were used to place the particles at a specific position along the probe. More recently, strategies where the microresonator is embedded in a feedback loop proved to be very effective in obtaining a more selective frequency response, which can be crucial to overcome the low quality factor typically associated with viscous media and the undesired forest of peaks.…”