Biosensors & Bioelectronics

Combinations of living cell-based biosensors and microdevices are attractive tools for real-time monitoring of gene expression profiling in a small population of cells involving small amount of analytes. However, due to the heterogeneous responsiveness of cells, cell-based biosensors have poor reproducibility and a low signal-to-noise (S/N) ratio. Previously, we constructed a “sensor cell”, a GFP reporter cell line containing an engineered Heart Shock Protein 70B’ promoter generated by stably transfecting mouse NIH/3T3 cells. In this study, we manipulated the cell density to overcome the lower signal and poor reproducibility using the sensor cells. We found that a cell density of 2 x 105 cells/cm2 provides good responsiveness of sensor cells that appears to be related to the G0/G1 phase of cell cycle. However, higher cell densities had a negative effect for on sensor performance. We also designed microdomains to regulate cell density. The GFP-positive rate of cells grown on domains at 2 x 105 cells/cm2 density was approximately 1.5 times higher than that of control cells. Our results suggest that cell density is an important factor for the design of cell-based biosensors with microdevices.

Fast growing used of QCM biosensor has been reported. It is well known that the QCM sensor responses both to mass or viscosity changes. In its operation as mass sensitive sensor, a QCM responses to the mass change per surface area. In the use of QCM biosensor, immobilization of the bio sensitive layer on top of the sensor surface is one of the importance factors. The immobilization of the biomolecule can be done directly on top of the sensor electrode or by using a coating material as supporting matrix. This experiment shows that the use of thick polystyrene coating with a rough surface resulted from air brush technique resulted in a significant improvement on the biomolecule immobilization compare to the polystyrene coating using spin coating method. As there is no chemical or physical modification on the polystyrene coating, the increasing numbers of the immobilized biomolecule merely a result of the surface geometry. The increasing number of immobilized biomolecule is caused by improving total surface area per perpendicular surface area of the sensor by introducing surface roughness. However, an appropriate care must be taken during the coating process to avoid over rough surface which in turn can heavily damp the QCM sensor.

This paper presents the use of a modified add-drop optical filter known as a PANDA microing resonator which can be designed on a chip. By using an optical tweezer, the required molecules can be trapped and moved to the required destinations, where finally, the required molecules can be retrieved (filtered) by using the tunable filter via the add-drop filter control. In application, storage molecules in the bottle in the designed chip can be trapped and moved to the required targets by optical tweezers, which can transport via the optical waveguide. Therefore, this technique can be used to form the molecular filter. This is a new technique and important for drug delivery, drug targeting and molecular electronics, which is described, the optical tweezer generation using a PANDA ring resonator is also reviewed. Results obtained have shown that the multivariable filter can be obtained by tunable trapping control.