However, the current cantilever used in liquid exhibits a small Q value, which makes the cantilevers work poorly in liquid. For example, the Q value of these cantilevers in liquid is barely more than 10 [12, 14]. This is really a challenge for cantilever-based biosensors since most of the samples to be tested are liquid.Different types of cantilevers made of different materials have been developed as transducers used in biosensors [12, 14, 17, 19-21]. In terms of actuating and sensing technologies, all the cantilevers can be classified into two types: passive and active. The passive cantilevers, such as silicon-based cantilevers, require a separated system to actuate the device and usually use a separated optic system to measure/monitor the vibration of the device.
On the other hand, the active cantilevers, such as piezoelectric-based cantilevers, can be easily actuated by simply applying a driving field, such as an electric field in the piezoelectric case, and the vibration behavior of the active cantilever can be easily sensed/monitored, such as by measuring impedance in the piezoelectric case. Due to the easiness and availability of the micro/nano-fabrication technology, silicon-based cantilevers are much more widely investigated than others. Additionally, silicon-based cantilevers exhibit a higher Q value than piezoelectric-based cantilevers.Recently, we introduced a novel type of active cantilever �C magnetostrictive microcantilever (MSMC) as a high-performance transducer for biosensor development [9]. The MSMC is wireless, works well in liquid, and exhibits a much higher Q value than other cantilevers [9].
In this article, the principle of the MSMC and technology used to characterize the MSMC are discussed and the recent development of the MSMC array is reported. The performance of the MSMC in different media is also reported. Additionally, the detection of Salmonella typhimurim in water was conducted to demonstrate the advantages of an MSMC as a transducer for biosensors.2.?Experimental Details2.1. Cantilever fabricationThe MSMCs used in the experiments are unimorph type cantilevers. A cantilever beam consists of two layers: one active layer and one inactive layer. The active layer is an amorphous magnetostrictive alloy, the Metglas? 2826 MB ribbon (Honeywell, Morristown, NJ) in thickness of 20 ��m.
The inactive layer is copper sputtered on the Metglas using magnetron DC sputtering. Prior to the deposition of copper layer (10~15 ��m in thickness) onto the polished Metglas, a chromium thin film of 100 nm in thickness was deposited on the Metglas to enhance the bonding between Metglas layer Carfilzomib and copper layer. The copper/Metglas bilayer was then cut into rectangles (strips) in different sizes. To fabricate the cantilevers, the bilayer strip was clamped at one end using a PMMA plastic holder to form the cantilever or MSMC.