Christopher D. Corso

An investigation of antibody immobilization methods employing organosilanes on planar ZnO surfaces for biosensor applications.

One critical aspect for the development of label-free immunosensors is the employment of highly uniform and repeatable antibody immobilization techniques. In this study, we investigated the use of two different silane molecules (3-glycidyloxypropyl)trimethoxysilane (GPS), and (3-mercaptopropyl)trimethoxysilane (MTS) for the immobilization of fluorescently labeled IgG antibodies on planar ZnO surfaces. The chemical modification of the surfaces was investigated using water contact angle measurements, AFM, and fluorescence microscopy. The results of the water contact angle measurements indicate increased surface hydrophobicity after treatment with GPS and MTS as compared to the control. Surface modification was further verified through AFM measurements which demonstrate an increased surface roughness and particle height after treatment with antibodies. The results of the fluorescence studies indicate that the immobilization protocol employing MTS produced 21% higher fluorescence on average with greater uniformity than the GPS-based protocol, which indicates a higher overall density in antibody coverage on the surface of the ZnO. Acoustic sensor tests were employed to confirm the functionality of sensors treated with the MTS protocol. The results indicate that the immobilization protocol imparts sensitivity and specificity to the ZnO-based devices.

Lateral field excitation of thickness shear mode waves in a thin film ZnO solidly mounted resonator

In recent years, interest in the development of highly sensitive acoustic wave devices as biosensor platforms has grown. A considerable amount of research has been conducted on AT-cut quartz resonators both in thickness excitation and in lateral excitation configurations. In this report, we demonstrate the fabrication of a ZnO solidly mounted resonator operated in thickness shear mode (TSM) using lateral field excitation of the piezoelectric film. Theoretical Christoffel equation calculations are provided to explore the conditions for excitation of a TSM wave in c-axis-oriented ZnO through lateral excitation. The existence of a TSM wave is verified through the comparison of theoretical and experimentally obtained acoustic velocity values from frequency versus thickness measurements and water loading of the resonators. A major strength of this design is that it incorporates a simple eight-layer, single-mask fabrication process compatible with existing integrated circuit fabrication processes and can be eas...

Lateral Field Excitation (LFE) of Thickness Shear Mode (TSM) Acoustic Waves in Thin Film Bulk Acoustic Resonators (FBAR) as a Potential Biosensor

Lateral field excitation (LFE) of a thin film bulk acoustic resonator (FBAR) is an ideal platform for biomedical sensors. A thickness shear mode (TSM) acoustic wave in a piezoelectric thin film is desirable for probing liquid samples because of the poor coupling of shear waves into the liquid. The resonator becomes an effective sensor by coating the surface with a bio- or chemi-specific layer. Perturbations of the surface can be detected by monitoring the resonance condition. Furthermore, FBARs can be easily fabricated to operate at higher frequencies, yielding greater sensitivity. An array of sensors offers the possibility of redundancy, allowing for statistical decision making as well as immediate corroboration of results. Array structures also offer the possibility of signature detection, by monitoring multiple targets in a sample simultaneously. This technology has immediate application to cancer and infectious disease diagnostics and also could serve as a tool for general proteomic research

A Thickness Shear Mode Zinc Oxide Liquid Sensor with Off-axis Excitation

A thickness shear mode acoustic sensor is developed based on a typical longitudinal mode electrode configuration through the use of a tuned acoustic mirror. The coupling of the electric field to a thickness shear mode occurs because of an off-axis electric field produced near the periphery of the top electrode. The existence of a lateral electric field component is verified through finite element simulations. The fabricated devices exhibit a Quality factor (Q) on average of 80 with an acoustic velocity of-3,086 m/s at 2.0 GHz. Sensor experiments are performed under liquid loading conditions, using glycerol-water solutions. The thickness shear mode resonance is monitored in real-time for a shift in frequency indicating sensitivity to the density-viscosity product. The highly sensitive mass sensor has the potential for use in biological sensing applications.

Passive sensor networks based on multi-element ladder filter structures

This work explores a novel acoustic resonator sensor system in a departure from the standard approach requiring an oscillator circuit to drive the resonance. The work is motivated by the need to monitor multiple sensors simultaneously in a near real-time manner. The system employs an arrangement of discrete resonators in a ladder network filter configuration. This arrangement establishes a passive structure in which the overall frequency response reports perturbations to individual resonators within the network. Here, we focus on the contribution of individual resonators to the overall response and explore methods for designing a passband response which has useful features for sensor experiments. It is concluded that an arrangement in which the resonant frequencies of the series and shunt resonators are offset results in a response that can be tracked during sensor experiments.

Stability of a RF sputtered ZnO solidly mounted resonator sensor in varying temperature and conductivity environments

It has been demonstrated that thickness shear mode acoustic wave devices have been extremely useful for liquid phase sensing applications, especially as biosensors. The quartz crystal microbalance is likely the strongest demonstration of this application to date. Recently, we reported a ZnO-based TSM device that is easily fabricated and operates at significantly higher frequencies than the QCM. To further validate the usefulness of the ZnO resonator as a strong candidate for biosensor applications, we report the stability of the device over varying temperature and sample conductivity. A modest thermal coefficient of resonant frequency is reported at ~25 ppm/degC. Further, it is demonstrated that the resonator exhibits reasonable stability over a range of sample conductivities (0.0 to 0.9 % wt/vol NaCl in DI H2O).