To answer the need for simplicity and fast time-to-result, Evasensor has devised the EVA-Technology, a biosensor which allows sensitive and easy-to-use fluorescence based measurement of multiple parameters simultaneously. An advanced optical readout technology based on evanescent fluorescence excitation is used for maximal sensitivity, highly optimized signal/noise performance. There is no crosstalk between the channels of the sensor chip. To avoid any carry over, the sensor chip is designed to contain eight fully separated, independent measurement wells. Biochemical compatibility of the EVA-Sensor Chips with existing protocols is achieved by using identical polystyrene material for manufacturing as used for standard microtiterplates.

For the readout, the EVA‑Chips are illuminated with excitation laser light under total internal reflection (TIR), generating an evanescent field at the bottom of the well. The evanescence penetrates only a few hundred nanometers into the liquid and only excites fluorescent molecules that are bound to the bottom of the well. This allows to reduce the volume required for measuring down to as little as 25µl - opposed to 100µl as required today in most tests. Continuous monitoring the increase of the emitted fluorescent light during 10 minutes, directly allows to determine the concentration of the analyte present the sample in quantitative manner.

Different applications can be obtained by attaching appropriate recognition molecules to the sensor surface through which analyte molecules present in the liquid can be detected specifically. To profit from the large number of different ELISA kits available today, existing ELISA kits can be modified directly by using a fluorescently labeled conjugate instead a of the enzyme conjugate substrate. In addition, the optical EVA readout allows to skip several time consuming steps and manipulations of the ELISA measurement procedure while maintaining its sensitivity.

Total Internal Reflection Fluorescence  

A TIRF-system as the EVA-Technology uses the optical phenomenon of evanescent waves to selectively illuminate and excite fluorophores in a restricted region close to the polymer-liquid interface. The evanescent wave is generated only when the incident light is totally internally reflected (TIR) at the  polymer-liquid interface. The evanescent electromagnetic field decays exponentially from the interface, and thus penetrates to a depth of only approximately 200 nm into the liquid sample medium. Thus the TIRF enables a selective visualization of surface regions such as in the EVA-Reader,