Abstract-We report the first monolithic tin oxide (SnO,) gas sensor realized by commercial CMOS foundry fabrication (MO-SIS) and post-fabrication processing techniques. The device is composed of a sensing film that is sputter-deposited on a silicon micromachined hotplate. The fabrication technique requires no masking and utilizes in-situ process control and monitoring of film resistivity during film growth. Micro-hotplate temperature is controlled from ambient to 500°C with a thermal efficiency of 8"C/mW and thermal response time of 0.6 ms. Gas sensor responses of pure SnO, films to H, and 0, with an operating temperature of 350°C are reported. The fabrication methodology allows integration of an array of gas sensors of various films with separate temperature control for each element in the array, and circuits for a low-cost CMOS-based gas sensor system.
BackgroundNanocarrier-based antibody targeting is a promising modality in therapeutic and diagnostic oncology. Single-walled carbon nanotubes (SWNTs) exhibit two unique optical properties that can be exploited for these applications, strong Raman signal for cancer cell detection and near-infrared (NIR) absorbance for selective photothermal ablation of tumors. In the present study, we constructed a HER2 IgY-SWNT complex and demonstrated its dual functionality for both detection and selective destruction of cancer cells in an in vitro model consisting of HER2-expressing SK-BR-3 cells and HER2-negative MCF-7 cells.MethodsThe complex was constructed by covalently conjugating carboxylated SWNTs with anti-HER2 chicken IgY antibody, which is more specific and sensitive than mammalian IgGs. Raman signals were recorded on Raman spectrometers with a laser excitation at 785 nm. NIR irradiation was performed using a diode laser system, and cells with or without nanotube treatment were irradiated by 808 nm laser at 5 W/cm2 for 2 min. Cell viability was examined by the calcein AM/ethidium homodimer-1 (EthD-1) staining.ResultsUsing a Raman optical microscope, we found the Raman signal collected at single-cell level from the complex-treated SK-BR-3 cells was significantly greater than that from various control cells. NIR irradiation selectively destroyed the complex-targeted breast cancer cells without harming receptor-free cells. The cell death was effectuated without the need of internalization of SWNTs by the cancer cells, a finding that has not been reported previously.ConclusionWe have demonstrated that the HER2 IgY-SWNT complex specifically targeted HER2-expressing SK-BR-3 cells but not receptor-negative MCF-7 cells. The complex can be potentially used for both detection and selective photothermal ablation of receptor-positive breast cancer cells without the need of internalization by the cells. Thus, the unique intrinsic properties of SWNTs combined with high specificity and sensitivity of IgY antibodies can lead to new strategies for cancer detection and therapy.
A monolithic CMOS microhotplate-based conductance-type gas sensor system is described. A bulk micromachining technique is used to create suspended microhotplate structures that serve as sensing film platforms. The thermal properties of the microhotplates include a 1-ms thermal time constant and a 10 C mW thermal efficiency. The polysilicon used for the microhotplate heater exhibits a temperature coefficient of resistance of 1.067 10 3 C. Tin(IV) oxide and titanium(IV) oxide (SnO 2 TiO 2) sensing films are grown over postpatterned gold sensing electrodes on the microhotplate using low-pressure chemical vapor deposition (LPCVD). An array of microhotplate gas sensors with different sensing film properties is fabricated by using a different temperature for each microhotplate during the LPCVD film growth process. Interface circuits are designed and implemented monolithically with the array of microhotplate gas sensors. Bipolar transistors are found to be a good choice for the heater drivers, and MOSFET switches are suitable for addressing the sensing films. An on-chip operational amplifier improves the signal-to-noise ratio and produces a robust output signal. Isothermal responses demonstrate the ability of the sensors to detect different gas molecules over a wide range of concentrations including detection below 100 nanomoles/mole. I. INTRODUCTION C HEMICAL microsensors represent one important application for microelectromechanical systems (MEMS) technology. Microhotplate devices belong to the MEMS family and can be fabricated in commercial CMOS technology using micromachining techniques [1]. Thermally isolated microhotplate structures can be utilized for conductance-type gas sensing [2] or as microscopic infrared sources [3]. The CMOS compatible process realizes a class of devices that are based on thermo-electromechanical effects and are compatible with existing very-large-scale-integration (VLSI) circuit design techniques [4]-[6]. In this paper, a monolithic integration of a gas sensor system based on CMOS-compatible microhotplate technology is presented. There are numerous applications avail-Manuscript
Microboiling events associated with the fast transient heating of a micrometer-scale metallic thin film
heater immersed in water have been studied. The effect of surface properties on the microboiling transients
was examined by modifying the heater surfaces with hydrophobic and hydrophilic alkanethiol self-assembled
monolayers (SAMs). The microheaters are thin films of platinum or gold-plated platinum that are
approximately tens of micrometers in width and hundreds of micrometers in length. The microheaters are
immersed in water and rapidly heated with short (<10 μs) square voltage pulses. The temperature−time
transients of the microheaters are obtained by measuring the heater resistance during the application of
the heating pulse. The bubble nucleation event associated with boiling is signaled in the temperature−time transient by an inflection point that results from a change in heat transfer when a vapor bubble forms
on the heater. Because of the extremely high heating rates (>108 K/s), superheating occurs and nucleation
temperatures as high as 296 °C have been measured in water. The surfaces of the gold-plated heaters were
coated with a series of hydrophilic [HO(CH2)6SH, HO(CH2)11SH, and HO(CH2)16SH] and hydrophobic
[CH3(CH2)7SH, CH3(CH2)11SH, and CH3(CH2)15SH] SAMs. Dramatic differences are observed in the
temperature−time transients of the hydrophilic versus hydrophobic SAM-coated microheaters. Microheaters
modified with hydrophobic SAMs exhibit lower boiling nucleation temperatures, more pronounced inflection
points, and higher average temperatures during microboiling. These differences can be rationalized by
considering simple models of surface wetting and surface vapor bubble formation.
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