Biosensors

Piezoelectric Cantilever Sensor


The piezoelectric cantilever sensor consists of a piezoelectric, e.g., PZT layer bonded to a nonpiezoelectric metal strip. Coating the cantilever surface with the antibody specific to a target antigen, we were able to detect the small mass change in the cantilever due to the binding of the target antigen to the antibody coated on the cantilever surface by monitoring the cantilever resonance frequency shift. This approach has been extended to directly detect and quantify biological substances such as cells and proteins in real time. With suitable receptor on the metal tip, detection of biological substances such as yeast cells, protein molecules (avidin, and avidin-biotin binding), bacteria E. coli and salmonella have been demonstrated. PECS is also excellent sensor for in-air detection. Array PEMS can be used to selectively detect gaseous species including biological and chemical warfare agents. The cantilever sensor has been used to detect gas species such as dimethyl methylphosphonate (DMMP), a nerve gas simulant. Utilizing the coating method that I developed, we have made freestanding PMN-PT tapes that were electroplated to form piezoelectric microcantilevers having a sensitivity of 10-12 g/Hz. Comparing to the current quartz microbalance (QCM) technology, the piezoelectric cantilever sensor has the advantages of miniaturization, forming arrays, and compatible with microelectronics. The piezoelectric cantilever sensor has the advantage that it can be miniaturized easily and incorporated in a small device. A PEMS has the driver, the vibrator, and the detector all in one device using simple electrical means. The sensor is compact and easily portable. A  PEMS of 50 microns in length can reach unprecedented femtogram sensitivities, smaller than the mass of a single virus or a fraction of a bacterium.

In addition, a PEMS can also measure a liquid’s viscosity and density over a wide range of viscosity, e.g., from less than 1 cp to larger than 4000 cp. A hand-held measuring unit has been built to complete the portable PEMS sensor system.


Piezoelectric Finger (PEF) for Breast Tumors

Cancerous tissues and tumors are stiffer than surrounding tissues. Measurement of tissue stiffness could aid early tumor/cancer location. Ability to measure tumor stiffness under shear in the DC mode, which none of the current technology could achieve, could greatly improve the accuracy of tumor malignancy diagnosis. The PEF that we developed is an “electronic finger” capable of accurately and non-destructively measuring both the Young’s modulus and shear modulus of tissues with gentle touches to the surface. A PEF can measure the Young’s modulus and shear modulus variations in tissues with less than one-millimeter spatial resolution to a depth of up to several centimeters, offering great potential for in-vivo early detection of diseases such as breast cancer tumor. The ability of a PEF to probe the interfacial properties of hard inclusions by comparing the DC compression and shear tests stands to greatly aid tumor malignancy test accuracy. Preliminary results indicated that a PEF is capable of identifying and locating small malignant tumors (less than 3 mm) that were missed by mammography, ultrasound and a physician’s palpation.