Ye Chang

Detection of Volatile Organic Compounds Using Microfabricated Resonator Array Functionalized with Supramolecular Monolayers

This paper describes the detection of volatile organic compounds (VOCs) using an e-nose type integrated microfabricated sensor array, in which each resonator is coated with different supramolecular monolayers: p-tert-butyl calix[8]arene (Calix[8]arene), 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine (Porphyrin), β-cyclodextrin (β-CD), and cucurbit[8]uril (CB[8]). Supramolecular monolayers fabricated by Langmuir-Blodgett techniques work as specific sensing interface for different VOCs recognition which increase the sensor selectivity. Microfabricated ultrahigh working frequency film bulk acoustic resonator (FBAR) transducers (4.4 GHz) enable their high sensitivity toward monolayer gas sensing which facilitate the analyses of VOCs adsorption isotherms and kinetics. Two affinity constants (K1, K2) are obtained for each VOC, which indicate the gas molecule adsorption happen inside and outside of the supramolecular cavities. Additional kinetic information on adsorption and desorption rate constants (ka, kd) are obtained as well from exponential fitting results. The five parameters, one from the conventional frequency shift signals of mass transducers and the other four from the indirect analyses of monolayer adsorption behaviors, thus enrich the sensing matrix (Δf, K1, K2, ka, kd) which can be used as multiparameter fingerprint patterns for highly selective detection and discrimination of VOCs.

Detection of Volatile Organic Compounds by Self-assembled Monolayer Coated Sensor Array with Concentration-independent Fingerprints.

In this paper, we have modeled and analyzed affinities and kinetics of volatile organic compounds (VOCs) adsorption (and desorption) on various surface chemical groups using multiple self-assembled monolayers (SAMs) functionalized film bulk acoustic resonator (FBAR) array. The high-frequency and micro-scale resonator provides improved sensitivity in the detections of VOCs at trace levels. With the study of affinities and kinetics, three concentration-independent intrinsic parameters (monolayer adsorption capacity, adsorption energy constant and desorption rate) of gas-surface interactions are obtained to contribute to a multi-parameter fingerprint library of VOC analytes. Effects of functional group’s properties on gas-surface interactions are also discussed. The proposed sensor array with concentration-independent fingerprint library shows potential as a portable electronic nose (e-nose) system for VOCs discrimination and gas-sensitive materials selections.

Silicon Nanowire Field-Effect Transistors—A Versatile Class of Potentiometric Nanobiosensors

Silicon nanowire field-effect transistors (Si-NW FETs) have been demonstrated as a versatile class of potentiometric nanobiosensors for real time, label-free, and highly sensitive detection of a wide range of biomolecules. In this review, we summarize the principles of such devices and recent developments in device fabrication, fluid integration, surface functionalization, and biosensing applications. The main focus of this review is on CMOS compatible Si-NW FET nanobiosensors.

Tuning the Resonant Frequency of Resonators Using Molecular Surface Self-assembly Approach

In this work, a new method to tune the resonant frequency of microfabricated resonator using molecular layer-by-layer (LbL) self-assembly approach is demonstrated. By simply controlling the polymer concentration and the number of layers deposited, precisely tuning the frequency of microfabricated resonators is realized. Due to its selective deposition through specific molecular recognitions, such technique avoids the high-cost and complex steps of conventional semiconductor fabrications and is able to tune individual diced device. Briefly, film bulk acoustic resonator (FBAR) is used to demonstrate the tuning process and two types of LbL deposition methods are compared. The film thickness and morphology have been characterized by UV-vis reflection spectra, ellipsometer and AFM. As a result, the maximum resonant frequency shift of FBAR reaches more than 20 MHz, meaning 1.4% tunability at least. The minimum frequency shift is nearly 10 kHZ per bilayer, indicating 7 ppm tuning resolution. Pressure cooker test (PCT) is performed to evaluate the reliability of LbL coated FBAR. Furthermore, applications for wireless broadband communication and chemical sensors of LbL coated FBAR have been demonstrated.

Detection of volatile organic compunds by high-Q piezotransduced single-crystal silicon bulk acoustic resonator arrays

This paper demonstrates a novel electronic nose (e-nose) system for volatile organic compounds (VOCs) detections which is composed of three high-Q piezotransduced single-crystal silicon bulk acoustic resonators (PSBARs) and functionalized with different self-assembled monolayers (SAMs). The different sensitivities of the PSBARs to VOCs are utilized to constitute unique identification codes for IPA, ethanol, hexane and heptane detections, and successfully realizing discriminations of different VOCs. Besides, ethanol vapor with concentration as low as 50 ppm has been successfully measured by SAM modified PSBAR.

VOC detection using multimode E-nose composed of bulk acoustic wave resonator and silicon nanowire field effect transistor array

Electronic nose (e-nose) is a useful tool for gas detection in environment monitoring, food industry and medical diagnosing. It utilizes sensor arrays to generate recognition pattern in identifying odor or specific analyte. Here a novel multimode e-nose is demonstrated for the detection of volatile organic compounds (VOCs) by integrating both gravimetric-sensitive sensor and electric-sensitive sensor. In this system, film bulk acoustic resonator (FBAR) is used to gain mass related information and silicon nanowire field effect transistor (Si-NW FET) to collect electrical related information for the analytes. The electronic nose is applied to discriminate the ethanol-hexane mixture and the concentration of each gas can be successfully calculated by simple math without using complex mathematic model. The hybrid e-nose system shows potential for the analysis of VOC mixture in the future.

Wireless gas sensing based on a passive piezoelectric resonant sensor array through near-field induction

We developed a wireless and passive piezoelectric resonant sensor for contimuous volatile organic compound detection. An equivalent circuit is proposed to model the sensing system, and Lamb wave resonators are adopted to demonstrate the wireless interrogation achieved by near-field inductive coupling. The wireless sensing system is employed to monitor the ethanol vapor concentration, and the sensitivity of the wireless sensor barely degrades compared to that of the wired one. Further, we simultaneously and wirelessly tracked several resonance frequencies of a monolithic sensor array, which demonstrates its potential for high-throughput and real-time point-of-care test.

Dual-Mode Gas Sensor Composed of a Silicon Nanoribbon Field Effect Transistor and a Bulk Acoustic Wave Resonator: A Case Study in Freons

In this paper, we develop a novel dual-mode gas sensor system which comprises a silicon nanoribbon field effect transistor (Si-NR FET) and a film bulk acoustic resonator (FBAR). We investigate their sensing characteristics using polar and nonpolar organic compounds, and demonstrate that polarity has a significant effect on the response of the Si-NR FET sensor, and only a minor effect on the FBAR sensor. In this dual-mode system, qualitative discrimination can be achieved by analyzing polarity with the Si-NR FET and quantitative concentration information can be obtained using a polymer-coated FBAR with a detection limit at the ppm level. The complementary performance of the sensing elements provides higher analytical efficiency. Additionally, a dual mixture of two types of freons (CFC-113 and HCFC-141b) is further analyzed with the dual-mode gas sensor. Owing to the small size and complementary metal-oxide semiconductor (CMOS)-compatibility of the system, the dual-mode gas sensor shows potential as a portable integrated sensing system for the analysis of gas mixtures in the future.

Film bulk acoustic resonator based gas sensor: A sensitive detector for gas chromatography

This paper reported a miniaturized sensitive gravimetric gas sensor based on film bulk acoustic resonator (FBAR). The sensitivity of the FBAR gas sensor was enhanced 10∼20 times after coating with nanomaterials (metal organic frameworks (MOFs)). A facile coating process of MOFs on FBARs was disclosed for the first time. Furthermore, utilizing FBAR sensors as detectors was firstly demonstrated in a prototype of chromatographic instrument by facile hyphenation of FBAR with commercial separation column.

Novel Gas Sensor Arrays Based on High-Q SAM-Modified Piezotransduced Single-Crystal Silicon Bulk Acoustic Resonators

This paper demonstrates a novel micro-size (120 μm × 200 μm) piezoelectric gas sensor based on a piezotransduced single-crystal silicon bulk acoustic resonator (PSBAR). The PSBARs operate at 102 MHz and possess high Q values (about 2000), ensuring the stability of the measurement. A corresponding gas sensor array is fabricated by integrating three different self-assembled monolayers (SAMs) modified PSBARs. The limit of detection (LOD) for ethanol vapor is demonstrated to be as low as 25 ppm with a sensitivity of about 1.5 Hz/ppm. Two sets of identification code bars based on the sensitivities and the adsorption energy constants are utilized to successfully discriminate isopropanol (IPA), ethanol, hexane and heptane vapors at low and high gas partial pressures, respectively. The proposed sensor array shows the potential to form a portable electronic nose system for volatile organic compound (VOC) differentiation.