Micron scale directional coupler as a transducer for biochemical sensing

Area of Science:

• Photonics
• Nanotechnology
• Biochemistry

Background:

• Directional couplers (DCs) are optical devices used for light manipulation.
• Quantum dots offer unique optical properties for bio-detection.
• Miniaturized sensors are crucial for point-of-care diagnostics.

Purpose of the Study:

• To investigate the use of microfabricated directional couplers for detecting DNA conjugated with quantum dots.
• To evaluate the performance of DCs with varying device lengths for optical signal detection.
• To explore the potential of DCs as a basis for miniaturized biochemical sensors.

Main Methods:

• Fabrication of micro-scale directional couplers.
• Conjugation of DNA with quantum dots.
• Optical signal detection using a CCD camera to monitor near-field patterns.
• Comparison of experimental results with theoretical and simulation data.

Main Results:

• Optical output signals from DCs correlated well with theoretical and simulation results across various device lengths.
• Even short 20 µm-long DCs detected optical intensity changes.
• A 1500 µm-long DC device demonstrated a 60× signal enhancement.
• Normalized signals exhibited cyclical changes for large refractive index variations (air/water).

Conclusions:

• Microfabricated directional couplers are effective for detecting DNA conjugated with quantum dots.
• DC devices show potential for miniaturized, two-dimensionally integrated biochemical sensing applications.
• The performance of DCs can be tuned by device length and refractive index changes.