This paper presents experimental results on the piezoresistance characterization of gate polysilicon available from two commercial CMOS processes. It is shown that the gate polysilicon is very strain-sensitive, and a gauge factor of about 25 can be readily achieved. This value can allow standard gate polysilicon to be used as a strain-sensing element for integrated microsensor applications. As an example, a sub-nanogram mass sensor was fabricated using commercially available CMOS technology and is presented. The device incorporates gate polysilicon of the CMOS process as the sensing material, and is subjected to low levels of strain in order to measure small masses (< 10−9 g). A potential application for this sensor is to monitor the growth of biological cell cultures in a liquid environment.
Hepatitis B surface antigen (HBsAg) concentrations were measured using a piezoelectric microcantilever sensor (PEMS) developed by the authors. The developed PEMS is label-free and detects the sensing signal electrically. It was designed to measure the mass of biomolecules attached to it using an accurate mass-microbalancing technique; its probe area is confined to the end of the cantilever, and its equivalent spring constant is relatively high to minimize the effect of changes in the surface stress when the biomolecules are attached to it. The “dip- and-dry” technique was used to enable the probe area of the sensor to react with reagents in controlled environmental conditions. HBsAg was detected by an immunoreaction whereas the reaction time, antibody density, and its area on the probe were kept at a constant level. The mass of the detected HBsAg was measured in the range of 0.1–100 ng/mL.
ABSTRACTThis paper describes the principle of array sensing with film bulk acoustic resonators (FBARs) for combinatory mass sensing and the use of the arrayed FBAR resonant mass sensor for parallel detection of protein-ligand reactions in liquid environment. Various ligands were immobilized on the gold layer on the FBAR’s sensing surface for selective protein detection. The FBARs of the arrayed FBAR were fabricated to have different resonant frequencies from one another by adding slightly varied amount of mass loading on the resonators. Results showed that the arrayed FBAR could detect specific bindings on its surfaces as the concentration of the target ligand was varied.
The bacterial cell is propelled through the liquid environment by means of one or more rotating flagella. The bacterial flagellum is composed of a basal body (rotary motor), hook (universal coupler), and filament (propellor). The filament is a rigid helical assembly of only one protein species — flagellin. The filament can adopt different morphologies and change, reversibly, its helical parameters (pitch and hand) as a function of mechanical stress and chemical changes (pH, ionic strength) in the environment.
The advent of the environmental SEM (ESEM) has made possible the examination of uncoated and untreated specimen surfaces in the presence of a gaseous or liquid environment. However, the question arises as to what degree the examined surface remains unaffected by the action of the electron beam. It is reasonable to assume that the beam invariably affects all specimens but the type and degree of effect may be totally unimportant for one class of applications and totally unacceptable for another; yet, for a third class, it is imperative to know how our observations are modified by the presence of the beam. The aim of this report is to create an awareness of the need to initiate research work in various fields in order to determine the guiding rules of the limitations (or even advantages) due to irradiation.
Measurement of Hepatitis B Surface Antigen Concentrations Using a Piezoelectric Microcantilever as a Mass Sensor
