Sampling and Mass Detection of a Countable Number of Microparticles Using on-Cantilever Imprinting

Abstract

Liquid-borne particles sampling and cantilever-based mass detection are widely applied in many industrial and scientific fields e.g., in the detection of physical, chemical, and biological particles, and disease diagnostics, etc. Microscopic analysis of particles-adsorbed cantilever-samples can provide a good basis for measurement comparison. However, when a particles-laden droplet on a solid surface is vaporized, a cluster-ring deposit is often yielded which makes particles counting difficult or impractical. Nevertheless, in this study, we present an approach, i.e., on-cantilever particles imprinting, which effectively defies such odds to sample and deposit countable single particles on a sensing surface. Initially, we designed and fabricated a triangular microcantilever sensor whose mass m0, total beam-length L, and clamped-end beam-width w are equivalent to that of a rectangular/normal cantilever but with a higher resonant frequency (271 kHz), enhanced sensitivity (0.13 Hz/pg), and quality factor (~3000). To imprint particles on these cantilever sensors, various calibrated stainless steel dispensing tips were utilized to pioneer this study by dipping and retracting each tip from a small particle-laden droplet (resting on a hydrophobic n-type silicon substrate), followed by tip-sensor-contact (at a target point on the sensing area) to detach the solution (from the tip) and adsorb the particles, and ultimately determine the particles mass concentration. Upon imprinting/adsorbing the particles on the sensor, resonant frequency response measurements were made to determine the mass (or number of particles). A minimum detectable mass of ~0.05 pg was demonstrated. To further validate and compare such results, cantilever samples (containing adsorbed particles) were imaged by scanning electron microscopy (SEM) to determine the number of particles through counting (from which, the lowest count of about 11 magnetic polystyrene particles was obtained). The practicality of particle counting was essentially due to monolayer particle arrangement on the sensing surface. Moreover, in this work, the main measurement process influences are also explicitly examined.

Tailored Microcantilever Optimization for Multifrequency Force Microscopy

“…This methodology drew inspiration from the particle-imprint method elucidated in the literature. [50,51] In our experiment, we first utilized the micro drop technique, [52] applying a specific quantity of sub-micron-sized droplets with a diameter of roughly 40 nm and a known concentration in water onto a hydrophobic silicon surface. To regulate the added nanoparticle's mass, adjustments were made to the concentration and droplet volume.…”

MEMS-Based Cantilever Sensor for Simultaneous Measurement of Mass and Magnetic Moment of Magnetic Particles

“…Moreover, to guarantee and render the sensors re-usable after adsorbing magnetic particles thereon, each cantilever was cleaned by sonicating in acetone for about 3-5 min. Before sonication, a cantilever was mounted on a specially designed metallic holder to mitigate the risk of breakage [32]. Thus, repetitive use of the cantilever sensor was possible.…”

“…Localized deposition of the MPs was conducted at a point towards the free-end of the sensing beam, aided by a digital camera. The added particle mass Δm proportionately changed the unloaded resonant frequency of the cantilever by Δf as follows [32]:…”

Self-Excited Microcantilever with Higher Mode Using Band-Pass Filter

“…Microresonators have a variety of scientific and industrial applications [1]. The measurement methods based on the natural frequency shift of a resonator or an actuator have been studied for a wide range of applications, including the detection of the microscopic mass and measurements of viscosity [2][3][4][5] and stiffness [6] and many others physical quantities [7]. Reducing the dimensions of the resonator increases the natural frequency of a resonator and achieves a high sensitivity and a high-frequency response in measurements.…”