Abstract
Due to a worldwide increased use of pharmaceuticals and, in particular, antibiotics, a growing number of these substance residues now contaminate natural water resources and drinking supplies. This triggers a considerable demand for low-cost, high-sensitivity methods for monitoring water quality. Since many biological substances exhibit strong and characteristic absorption features at wavelengths shorter than 300 nm, UV spectroscopy presents a suitable approach for the quantitative identification of such water-contaminating species. However, current UV spectroscopic devices often show limited light-matter interaction lengths, demand sophisticated and bulky experimental infrastructure which is not compatible with microfluidics, and leave large fractions of the sample analyte unused. Here, we introduce the concept of UV spectroscopy in liquid-filled anti-resonant hollow core fibers, with large core diameters and lengths of approximately 1 m, as a means to overcome such limitations. This extended light-matter interaction length principally improves the concentration detection limit by two orders of magnitude while using almost the entire sample volume—that is three orders of magnitude smaller compared to cuvette based approaches. By integrating the fibers into an optofluidic chip environment and operating within the lowest experimentally feasible transmission band, concentrations of the application-relevant pharmaceutical substances, sulfamethoxazole (SMX) and sodium salicylate (SS), were detectable down to 0.1 µM (26 ppb) and 0.4 µM (64 ppb), respectively, with the potential to reach significantly lower detection limits for further device integration.
Highlights
The contamination of drinking water and water supplies by otherwise widely accepted substances, such as pharmaceuticals, forms one severe threat of our modern society
The operation principle of the ARHCF can be understood on the basis of interface reflection: assuming a plane wave impinging on a thin silica film of thickness identical to that of the core-ring, close-to-unity reflection canof bethickness obtainedidentical due to the interference between the two waves reflected impinging on a thin silica film to that of the core-ring, close-to-unity reflection canat interfaces, i.e., initial wave is anti-resonant with the mode inside film
The resulting value for the experimentally determined absorbtivity (ε A,exp =11,351 M−1 cm−1 ) agrees well with that obtained from simulations (ε A,sim =11,296 M−1 cm−1 ) and clearly confirms that the concept of UV spectroscopy using
Summary
The contamination of drinking water and water supplies by otherwise widely accepted substances, such as pharmaceuticals, forms one severe threat of our modern society The presence of such substances presents unforeseen consequences for human health, such as direct intoxication or, even more severe, the formation of multi-resistant pathogens [1,2,3,4], potentially rendering currently used antibiotic treatments ineffective. These highly relevant issues define a clear need to develop low cost, straightforward-to-apply, and highly sensitive, methods for water monitoring [5]. The linear absorption of light inside a medium, that is transparent over the device length considered and includes species which strongly absorb, is given by the well-known Beer–Lambert law: P
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