On-Chip Photothermal Analyte Detection Using Integrated Luminescent Temperature Sensors

Area of Science:

• Microfluidics
• Optical Sensing
• Photothermal Detection

Background:

• Optical absorbance detection sensitivity is limited by short path lengths in microfluidic devices.
• Photothermal detection offers an alternative with enhanced sensitivity.
• Integrated luminescent temperature sensors provide a novel approach for microscale sensing.

Purpose of the Study:

• To develop a new photothermal absorbance measurement technique using integrated luminescent temperature sensors within microfluidic channels.
• To quantify the absorbance of analytes using these integrated sensors.
• To demonstrate the application of this technique for sensitive optical detection on the microscale.

Main Methods:

• Photopolymerization of NOA 81 prepolymer doped with a ruthenium(II) temperature probe to create integrated sensing spots (26 ± 3 μm).
• Utilizing a 532 nm laser for excitation and measuring temperature changes via luminescent spots.
• Investigating the influence of flow rate, laser power, and analyte concentration (Amaranth dye, nitrite).

Main Results:

• Sensing spots achieved a temperature resolution of < 0.3 K (20–50 °C).
• Linear calibration curve obtained for Amaranth concentration and temperature signal.
• Limit of detection (LOD) of 13 μM for Amaranth and 26 μM for nitrite, with a minimal detectable absorbance of 3.2 × 10⁻³ AU.

Conclusions:

• The developed photothermal absorbance measurement with integrated luminescent sensors offers a sensitive and potentially spatially resolved detection method.
• This technique is highly promising for micro- and nanoscale optical absorbance detection.
• Demonstrated successful application in microreactor-based nitrite analysis with rapid assay time.