Single drop Whole Blood Diagnostics: Portable Biomedical Sensor for cardiac. Troponin I detection

Transcription

1 Single drop Whole Blood Diagnostics: Portable Biomedical Sensor for cardiac Troponin I detection Indu Sarangadharan 1, Shin-Li Wang 1, Revathi Sukesan 1, Pei-chi Chen 1, Tze-Yu Dai 1, Anil Kumar Pulikkathodi, Chen-Pin Hsu 1, Hui-Hua Kenny Chiang 3, Lawrence Yu-Min Liu *4,5, Yu- Lin Wang* 1, 2 1. Institute of Nanoengineering and Microsystems, National Tsing Hua University, Hsinchu, 300, Taiwan, R.O.C. 2. Department of Power Mechanical Engineering, National Tsing Hua University, Hsinchu 300, Taiwan, R.O.C. 3. Department of Biomedical Engineering, National Yang Ming University, Taipei 112, Taiwan, R.O.C. 4. Division of Cardiology, Department of Internal Medicine, Mackay Memorial Hospital, Hsinchu 300, Taiwan, R.O.C. 5. Department of Medical Science & Institute of Bioinformatics and Structural Biology, National Tsing Hua University, Hsinchu 300, Taiwan, R.O.C. Supplementary Information Fabrication of sensor array chip Sensor measurement Immunoassay protocols Sensor regeneration S-1

2 Fabrication of sensor array chip The gold electrode array is fabricated on a thermo-curable epoxy resin. The epoxy resin is poured on a PDMS mold and cured at 125 and 165 for 1 and 1.5 hours respectively. Post curing, the epoxy substrate is peeled off from the PDMS mold and patterned using photolithography for metal deposition. Electron beam (e-beam) evaporator is used to deposit Ti (200 Å) and Au (2000 Å) on the epoxy substrate and lift off is carried out in acetone. The gold electrodes are passivated using photoresist and sensing regions are opened using photolithography. Each gold electrode pair consists of a reference gate electrode and a sensing electrode. The reference gate electrode is connected to V g supply and sensing electrode is connected to the gate terminal of the MOSFET. The openings on the reference gate electrode and sensing electrode are 3600 µm 2, separated by a gap of 185 µm. Sensor measurement Portable biosensor system is used to measure the sensor characteristics. The system has a microcontroller unit, signal acquisition and read out circuitry and USB interface to connect with laptop to display the results. The MOSFET used in this study is N-Channel Depletion-Mode DMOS FET (LND150). The user interface software allows two modes of operation: single and burst. In single mode, one measurement data is acquired whereas in burst mode, multiple, repeated measurement data are acquired. Burst mode of operation has been used in this study throughout. A short duration gate pulse with a width of 100 µs and amplitude of 1 V is applied as the gate bias to the reference electrode. A steady DC bias of 2 V is applied as the drain-source voltage during device operation. Figure S1 shows the test parameters used for measurement to define the bias voltages and current gain calculations carried out by the prototype system. Figure S2 shows the typical drain current response from sensor obtained in 1X PBS (with 4% BSA). S-2

3 S-3 Figure S1 Test parameters and current gain calculation by prototype system.

4 Figure S2 Drain current versus time graph for ctni detection in 1X PBS with 4% BSA. Immunoassay protocols Figure S3 Assay protocols involved in ctni detection using portable FET biosensor system: Drop blood on sensor array chip; during sample incubation period (5 minutes), up turn the device so that it faces downwards, for gravitational separation of blood cells; After 5 minutes carry out electrical measurement using the software installed in the personal computer and obtain results instantaneously. In the current device format, 10 µl of blood sample is sufficient to cover all the sensing areas on the chip and up to 100 µl of blood sample has been tested to show a stable inverted droplet S-4

5 formation. However, such large quantity of sample is not required. Our sensor is intended to test fingertip blood which will be brought in to the sensing region via capillary channel without any external actuation. This requires only small quantity of sample, about ~10 µl. The capillary channel further prevents falling off of the inverted droplet. Sensor regeneration After testing the sensor with ctni containing solution, the sensor is repeatedly washed in gentle protein elution buffer (ph 6.6) and 1X PBS, alternatively. The sensor baseline is verified electrically to confirm sensor regeneration. Figure S4 Sensor regeneration. The sensor baseline measured in 1X PBS environment for ctni detection in clinical blood samples with (a) device facing down (b) device facing up. S-5