Chemical sensors have gained importance in the past decade for applications that include homeland security, medical and environmental monitoring, and food safety. A desirable goal is the ability to simultaneously analyze a wide variety of environmental and biological gases and liquids in the –eld and to be able to selectively detect a target analyte with high speci–city and sensitivity. In the area of detection of medical biomarkers, many different methods have been employed, including enzyme-linked immunosorbent assay (ELISA), particle-based £ow cytometric assays, electrochemical measurements based on impedance and capacitance, electrical measurement of microcantilever resonant frequency change, and conductance measurement of semiconductor nanostructures, gas chromatography (GC), ion chromatography, high-density peptide arrays, laser scanning quantitative analysis, chemiluminescence, selected ion £ow tube (SIFT), nanomechanical cantilevers, beadbased suspension microarrays, magnetic biosensors, and mass spectrometry (MS) [1-9]. Depending on the sample condition, these methods may show variable results in terms of sensitivity for some applications and may not meet the requirements for a handheld biosensor.