An integrated optoelectronic chip for sensing aromatic hydrocarbon contaminants in groundwater

The local evanescent array coupled (LEAC) chip-scale sensor is demonstrated for rapid detection of benzene, toluene and xylenes (BTX) in water at sub-ppm concentrations with minimal sample preparation. BTX analytes are found to concentrate into the chip's Teflon AF upper cladding sensing region, causing an increase in refractive index, which modulates evanescent coupling into the chip's integrated photodetector array. Integration of the photodetector array simplifies system instrumentation and permits incorporation of an on-chip photocurrent reference region in the immediate vicinity of the sensing region, reducing drift due to temperature fluctuations. A nearly linear response is demonstrated for all tested concentrations between 1 ppm and 30 ppm, and a limit of detection of 359 ppb, 249 ppb and 103 ppb is demonstrated for benzene, toluene and xylene in water, respectively. The effect of matrix interference contaminants is investigated and a method for identifying individual contaminants based on extraction of the contaminant's diffusion coefficient is presented.