Search

An electrophoretic cantilever-based nanoparticle (NP) sensor was described and evaluated for personal monitoring of occupational exposure at indoor environment. Measurements performed under defined NP concentrations in a conditioned chamber confirmed the feasibility of the measurement principle. For the first laboratory sample of the sensor cyclic switching between NP sampling and frequency tracking revealed settling times of 5 min and 1.5 min, respectively, until stable conditions were reached. Using an enhanced design of the sampling head this response time was considerably reduced to 20 s. With a total device volume of 540 cm 3 , weight of 375 g, and power consumption of 1.25 W the fully integrated pocket-sized system can be easily held or worn, e. g., by workmen in nanotechnology industry during their working shifts. [ABSTRACT FROM AUTHOR]

Vertically aligned silicon nanowire (SiNW)-based resonators were fabricated and utilised to detect aerosol nanoparticles (NPs) by measuring their resonant frequency shifts caused by the additional mass of trapped NPs. Inductively coupled plasma cryogenic dry etching and multiple thermal oxidations are used in the fabrication of silicon nanowire (SiNW) arrays. The SiNWs were coated with gold for contacting to the homebuilt electrostatic NP sampler to collect the flowing NPs. In order to have a dynamic resonance operation in the frequency measurement system, a piezoelectric shear actuator was mounted onto the SiNWs. Examined in a TiO2 aerosol sampling with a total concentration of ~8500 NP/cm³, the fabricated sensor exhibited its feasibility as a nanobalance to measure aerosol NP mass at the femtogram level with a mass sensitivity of 7.1 Hz/fg and a mass resolution of 31.6 fg. The NP sampling efficiency of the developed miniaturised NP sampler was found to be three times higher than that of the commercial nanometer aerosol sampler (NAS, TSI 3089). An ultrasonic removal method was used to detach the adhered NPs and further extend the operating life of the sensor. [ABSTRACT FROM AUTHOR]

In this article, WE FOCUS ON silicon nanowire (SiNW)-based resonators that were fabricated and employed to sense aerosol nanoparticles (NPs) by measuring resonant frequency shifts induced by the mass of stuck NPs. The fabrication of SiNW arrays was performed using inductively coupled plasma (ICP) cryogenic dry etching and multiple thermal oxidations. The SiNWs were coated with gold (Au) for contacting to the homebuilt electrostatic NP sampler to collect the flowing NPs. A piezoelectric shear actuator mounted in the frequency measurement system was used to excite the SiNW sensors into resonance. Tested in a titanium dioxide (TiO2) aerosol sampling with a total concentration of ~8,500 NPs/cm3, the sensor displayed its feasibility as a nanobalance to detect aerosol NPs in the femtogram scale with a mass sensitivity of 7.1 Hz/fg and a mass resolution of 31.6 fg. To extend the operating life of the sensor, an ultrasonic removal method was used to detach the adhered NPs. [ABSTRACT FROM PUBLISHER]

The development and real-time performance test of a fully integrated low-cost handheld cantilever-based airborne nanoparticle (NP) detector (CANTOR-2) are described in this paper. The device is the enhancement of the previously developed cylindrical electrophoretic NP sampler (CANTOR-1), which is used for direct-reading of exposure to airborne carbon engineered nanoparticles (ENPs) in indoor workplaces. All components of the proposed detector can be divided into two main units depending on their packaging placements (i.e., the NP sampler head and the electronics mounted in a handy-format housing). For the NP sampler, a miniaturized electrophoretic aerosol sampler created in a cubical shape and an electrothermal piezoresistive resonant silicon cantilever mass sensor are employed for collecting the ENPs from the air stream to the cantilever surfaces and measuring their mass concentration, respectively. To realize a real-time measurement, a frequency tracking system based on phase-locked loop (PLL) is built and integrated to the device. From the device calibration, a good correlation of the CANTOR-2 data is found with the fast mobility particle sizer (FMPS, TSI 3091) reference at a precision of 8–14%. By having a total device volume of 540 cm 3 , weight of 375 g, and power consumption of 1.25 W in the current version, this developed CANTOR-2 provides a very good portability for being used as a personal airborne NP monitoring device, which can be easily held or worn by workers during their activities. [ABSTRACT FROM AUTHOR]

Abstract: This work demonstrates mass measurement of airborne titanium dioxide (TiO2) engineered nanoparticles (ENPs) using silicon resonant nanopillar sensors by monitoring resonant frequency shifts induced by the mass of trapped ENPs. Inductively coupled plasma (ICP) cryogenic dry etching and thermal oxidation have been used in the sensor fabrication. A piezo shear actuator and an electrostatic precipitator are utilized to excite the nanopillars in resonant mode and collect the flowing TiO2 ENPs, respectively. By using the fundamental bending frequency, the sensor can achieve a mass sensitivity of 7.22Hz/fg, which enables its application to a nanobalance to detect airborne ENPs in the femtogram mass range. Two methods of ENP removals (i.e., polydimethylsiloxane (PDMS) and ultrasonic cleanings) have also been performed to remove the adhered ENPs, thus efficiently extending the operating life of the sensor. This developed sensor is targeted to be implemented as a handheld ENP monitoring device at workplaces. [Copyright &y& Elsevier]

Abstract: Photoresist-based nanoparticle (NP) removal is evaluated as an approach to extend the life time of silicon resonant cantilever-based mass sensors for airborne NP monitoring. Integrated with a miniaturized electrostatic NP sampler, the cantilever can collect and detect airborne NP mass. Prior to airborne NP sampling, the cantilever surface is covered by a sacrificial layer of photoresist. Within a lift-off process of wet cleaning, the photoresist layer is removed together with the trapped NPs with cleaning efficiencies of ∼95–99%. The resonant frequencies and the quality factors (Q-factors) of the cantilevers are characterized for different thicknesses of the photoresist layers given by their viscosities. The proposed recycling technique is found to be most effective when a thin photoresist film is used. By using higher order resonant modes, Q-factors of more than 1000 in air are maintained even after the photoresist coating. As necessary for an application under workplace conditions, the limitations of the sensor sensitivity influenced by the environment, i.e., ambient temperature and relative humidity (rH), are also measured. [Copyright &y& Elsevier]

Abstract: A portable cantilever-based airborne nanoparticle detector (CANTOR) was designed and manufactured for detecting engineered nanoparticles (ENPs) in workplace air by monitoring the resonant frequency shift induced by the mass of the particles trapped on the cantilever resonator. The CANTOR consists of two main modules, i.e., a silicon resonant cantilever sensor and a miniaturized electrostatic ENP sampler. Tested in 15-min aerosol sampling with ∼100nm carbon-based ENPs having a concentration of ∼6000NPs/cm3, the sensor exhibited a mass sensitivity of 36.51Hz/ng when the second resonant mode was used. Two simple cleaning methods, i.e., dry and wet cleanings, to remove the attached ENPs were successfully demonstrated in order to extend the operating life of the sensor. [Copyright &y& Elsevier]

Abstract: A silicon resonant cantilever sensor is developed for detection of airborne nanoparticles (NPs) by monitoring the change in resonant frequency induced by an additional mass of trapped NPs. A piezoelectric stack actuator and a piezoresistive strain gauge are involved in the sensor system in order to actuate and detect the oscillation of cantilever sensor, respectively. An electrostatic precipitator is employed to trap the NPs on the cantilever surface. The proposed sensor reveals a mass sensitivity of 10Hz/ng and a quality factor of 1206 while operated in the fundamental flexural mode. As necessary for an application under workplace conditions the limitations of the sensor sensitivity imposed by the environment are investigated, i.e., the influences of temperature, relative humidity, and pressure on the sensor are measured. [Copyright &y& Elsevier]