Authors: B.L. Weeks, J. Camarero, A. Noy, A.E. Miller, L. Stanker and J.J. De Yoreo
Affilation: Lawrence Livermore National Laboratory, United States
Pages: 123 - 125
Keywords: sensors, salmonella, AFM
Increasing efforts have been put into the developments of cantilever-based micro sensors. These devices show fast responses, high sensitivity, and are suitable for mass production. Currently, they are mainly applied for quality and process control, diagnostic biosensing for medical analysis, fragrance design (artificial noses), and gas analysis. The application of single cantilever sensors to determine quantities below the detection limits of equivalent classical methods such as thermal, chemical, stress, mass loading or magnetic signals has been demonstrated in the literature. The cantilevers sensors can be fabricated from either silicon or silicon nitride and are either rectangular or triangular in shape. The small size of this cantilever-based sensor leads to significant advantages in the absolute device sensitivity. Precise measurement of the deflection of the end of the cantilever is achieved through an optical sensing arrangement. Here, a laser is focused onto the end of the cantilever and the bending of the beam is detected as the movement of the reflected laser spot on a position-sensitive photodiode. Detection sensitivity of less than one Ångström is readily achieved. Detection of an analyte can be achieved through several possible mechanisms. Binding of an analyte to the cantilever surface will cause an easily detectable change in the surface stress. A biochemical reaction at the cantilever surface will produce a temperature gradient also detectable through the bending of the cantilever. Furthermore, a change in mass load on the order of 1 pg can be detected as a change in the resonant frequency of the cantilever. To detect biomolecules one side of the cantilever has to be coated with a detector film that has specific affinity to the biomolecules under investigation. Binding events are readily detectable through the resulting change in the surface stress. Experimental results will be presented for the detection of specific strains of Salmonella. By coating one side of the cantilever with monoclonal antibodies the cantilevers show specific and selective detection of individual strains (Figure 1). By subsequent SEM imaging of the cantilever after exposure to the pathogen shows the Salmonella only adheres to the side of the cantilever with the antibody and shows detection limits in the range of 25 organisms for detection (Figure 2). In conclusion, cantilever detectors present many attractive features for pathogen detection including compactness, high sensitivity, and operation in multiple environments. Work to date has demonstrated that with the proper functionalization, these detectors can even discriminate amongst multiple strains of a single pathogen. In addition, we will present methods such as dip-pen nanolithography, which allows for specific and spatial functionalization of the cantilever surface.