Presented is a label-free biosensor based on a film bulk acoustic resonator (FBAR) to detect one of the cancer markers of alpha-fetoprotein (AFP). The FBAR consisted of a ZnO piezoelectric stack and works near 2.1 GHz. The monoclonal anti-AFP antibody was coated on the surface of the piezoelectric stack as the special bioprobe. Experimental results demonstrate that the FBAR based biosensor can detect AFP antigen successfully without chemical or fluorescent labelling. The minimum detectable AFP concentration of the proposed biosensor is 1 ng/ml with high selectivity. The advantages of this sensor, including the sample fabrication process, ease of detection method, low cost, high sensitive and high-throughput, mean that it has much promise in cancer diagnosis.Introduction: To accurately diagnose and closely monitor complex disease such as cancer, the quantitative detection of multiple serological markers is necessary. In the last few years, there has been growing interest in label-free biosensors using optical and gravimetric systems, such as surface plasmon resonance (SPR) [1], quartz crystal microbalance (QCM) [2], surface acoustic wave (SAW) devices [3] and microcantilevers [4] to detect the presence of specific compounds with selectivity and quantity. Unfortunately, for cancer diagnosis, low-cost, highly sensitive, high-throughput and easily operated technology is still in the developmental stage and requires significant improvements for practical applications.The micromachined monolithic film bulk acoustic resonator (FBAR) makes use of standard silicon technology, and provides low cost and high throughput using a simple electrical detection method with no need of expensive optical apparatus and labelling with fluorescent or adioactive molecules. With a working resonance of 2 to 10 GHz, the FBAR has a minimum detectable mass change in the range of 10 ng/cm 2 , which is several orders of magnitude lower than that of QCM, the working resonance of which is in several megahertz. To date, many attempts to use the FBAR for biochemical applications have been made, with remarkable results [5,6].In the work reported in this Letter, we developed a label-free biosensor based on an FBAR to detect alpha-fetoprotein (AFP). In clinical diagnosis, AFP is a serological marker for hepatocellular carcinoma (HCC), which is the fifth most common cancer and the third leading cause of cancer death worldwide. To enhance the early diagnosis level of HCC, a biosensor applied for AFP detection would better feature the concentration detection limit of less than 10 ng/ml, that is, at ng/ml level [7]. Based on the very low detectable mass change of an FBAR, our FBAR based biosensor can detect the presence of 1 ng/ml AFP antigen successfully.

A highly sensitive, rapid and convenient biosensor based on film bulk acoustic resonator has been developed for detection of pesticide residues in agricultural products. When the pesticide molecules are bound to the immobilised antibodies on the resonator sensing surface, the resonant frequency is obviously reduced because of additional mass. Trace pesticide in the solutions was detected through real-time monitoring of the resonant frequency during antigen-antibody reactions on the resonator surface. Using the proposed biosensor, realised is a convenient and rapid detection process (less than 1 min) and a remarkable low detection limit (ppb level) for the pesticide. On the basis of the sensing performances, the film bulk acoustic resonator shows promising applications for food safety guarantees.Introduction: Food safety has received more and more attention worldwide. Now, a number of portable biosensors based on various transduction mechanisms, including quartz crystal microbalances (QCMs) [1], enzyme-linked immunosorbent assays (ELISAs) [2], surface plasmon resonances [3], electrochemical sensors [4] and microcantilevers [5], have been used in routine detection of food security. However, these devices cannot be configured easily for rapid, simple and low-cost detection because of their large sizes, complex operations or sophisticated optical equipments.Over the past five years, many attempts to use film bulk acoustic resonators (FBARs) for sensing applications have been made with remarkable results, including gas sensing [6], ultraviolet light sensing [7] and biological detection [8]. The FBARs make use of microelectromechanical systems technology, thereby enabling the integration of the sensors with their electronic circuits and the microfluidic devices into a single chip. Furthermore, as a universal mass-sensitive platform, typical FBARs work in gigahertz range and offer a sensitivity increase of more than three orders of magnitude over the classic mass-sensitive QCMs [9].

Presented is a lateral field excited film bulk acoustic resonator for realtime sensing of protein -ligand interaction using the biotin -streptavidin system as a model. The film bulk acoustic resonator works at 2 GHz in shear mode. For biosensing, the biotin was immobilised on one face of the resonator as the probe. The resonant frequency of the biotin-immobilised device drops rapidly at first and gradually reaches equilibrium when exposed to the streptavidin solutin due to the biotin -streptavidin interaction. Consequently, the lateral field excited film bulk acoustic resonator can be used to study the kinetics of protein -ligand interaction without the use of labelling or molecular tags. The proposed device shows promising applications for disease diagnostics, prognosis, and drug discovery.Introduction: In the field of biotechnology and pharmaceutics, one of the critical parts is understanding the kinetics of protein-ligand interactions. Traditional studies for protein -ligand interactions require chemical, fluorescent or radioactive labelling, which usually compromise the protein activity and do not give real-time interaction information. Therefore, label-free biosensors have received much attention because they can directly measure biomolecular interactions in realtime and in situ.Over the past ten years, the commercial success of film bulk acoustic resonators (FBARs) in radio frequency communication has motivated researchers to explore their applications for label-free and high sensitive biochemical sensing [1,2]. FBARs make use of standard IC fabrication technology, thereby realising the ability to inexpensively combine a number of sensors on a chip and integrate them with the analytical circuits. The applications of FBARs for real-time biochemical detection require their operation in shear mode due to the minimal damping in the liquid-solid interface. Some investigations demonstrated quasishear mode FBARs based on inclined c-axis oriented ZnO or AlN piezoelectric films coupled with the electrodes which are situated on opposite sides of the films [3,4]. An apparent deficiency of the quasi-shear resonator is the existence of an amount of longitudinal component in the wave polarisation, which inevitably leads to acoustic energy leakage into the liquid. To alleviate this problem, the lateral electric field is employed to excite pure shear mode in ZnO or AlN films [5].In this reported work, we fabricated a lateral field excited FBAR and used it for real-time sensing of protein-ligand interaction. For a demonstrational study, the biotin -streptavidin system was chosen as a model since such a system has been well characterised. High binding affinity and stability makes the biotin -streptavidin system very useful in many biotechnological applications such as in affinity separation, in diagnostics, for molecular tagging, for imaging application, biomolecular delivery, and in the characterisation of surface bound biomolecular species.