David Chauvin1, Isabelle Ledoux-Rak1 and Chi Thanh Nguyen1,*
1Laboratoire de Photonique Quantique et Moléculaire, UMR 8537, Ecole Normale Supérieure Paris-Saclay, CentraleSupélec, CNRS, Université Paris-Saclay, 61 avenue du Président Wilson 94235 Cachan, France
* Email: ctnguyen@lpqm.ens-cachan.fr; Tel.: +33-147405557
We report in this paper a new design and realization of a differential label-free optofluidic sensor based on polymeric vertically coupled microresonators for biochemical sensing. Label-free sensing based on optical polymeric microresonators has shown a very high performance in terms of detection limit [1]. When integrated into a microfluidic circuit to form an optofluidic device, it can provide an efficient and accuracy real-time monitoring of surface sensing and chemical reaction kinetics detection [2, 3]. But when using a single transducer configuration, the transduction signal of an optofluidic sensor is perturbated by various phenomena such as thermal drift, spikes of microfluidic pressure, mechanical vibration parasites, intensity variation of optical source. These perturbations severely reduce the accuracy of sensing and then the sensor detection limit. Differential measurement permits to overcome these perturbations and therefore to improve sensor performances. The differential measurement principle is based on a simultaneous comparison of an analyte transduction signal with a reference transduction signal measured under the same physical conditions. If these two signals are submitted to the same external perturbations, we can extract the net sensing signal by subtracting the analyte transduction signal from the reference signal. To assure that these two signals are in the same experimental conditions, the design, the fabrication and the set-up of the optofluidic sensor should be optimized.
A schematic view of the device is illustrated in Figure 1, and the concatenation of microscope photographs of the optical integrated device is presented in Figure 2. This device, composed of one Y-branch directional coupler and two identical vertically coupled microracetracks, was made of polymers (SU-8 photoresist and Cytop fluorocopolymer) deposited onto a silica lower cladding covering a silicon substrate. Microfluidic channels were fabricated with another polymer (PDMS) and covered the optical integrated circuit by applying a pressure via a specific mechanical set-up. The microfluidic flows injected into two sensor channels were provided by a microfluidic station (pump and two electrovalves). The optical detection setup was realized with two separated identical photodetectors. The optical source was a tunable laser emitting at 1500-1640 nm wavelengths.
The differential optofluidic sensor has demonstrated a real-time automatic correction of the long-term thermal drift and also of the short-term external perturbations in its response. Figure 3 presents the results of a homogeneous detection of glucose solution (27.9 mM glucose in deionized water) by the sensor. On the left, we observed a thermal drift on the transduction signals extracted from measurement and reference microracetracks and on the right, the real-time differential signal. In Figure 4 are presented the result of an automatic correction of short-term interferences (spikes on the signals) on the sensor response. We can apply also this sensing scheme for the surface detection in order to overcome not only external perturbations but also some non-specific effects of surface detection. A new multiplex sensing using our optofluidic sensor for surface detection of the couple streptavidin-biotin is going to be realized.
Fig.1 Schematic view of the differential label-free optofluidic sensor based on polymeric microracetracks.
Fig. 2 Concatenation of photographs under microscope of the polymer-based microracetracks device.
Fig. 3 Optical response of the sensor with thermal drift (left) and its differential response (right).
Fig. 4 External perturbations on the transduction signals of the sensor (left) and of its differential response (right).
REFERENCES:
[1] Delezoide, M. Salsac, J. Lautru, H. Leh, C. Nogues, J. Zyss, M. Buckle, I. Ledoux-Rak, and C. T. Nguyen, "Vertically coupled polymer microracetrack resonators for label-free biochemical sensors", Phot. Technol. Lett., 2012, 24, 270-272.
[2] Delezoide, J. Lautru, J. Zyss, I. Ledoux-Rak, and C. T. Nguyen, "Vertically coupled polymer microresonators for optofluidic label-free biosensors", Proc. of SPIE, 2012, 8264, 826416-13.
[]3 Chauvin, I. Ledoux-Rak and C.T. Nguyen, "Optimizing detection limits of optical resonator based sensors by optimization of real-time measurement of resonators response", Proc. of SPIE, 2016, 9899, 98991J.
