Water pollution by heavy metals through the discharge of industrial waste water becomes a worldwide environmental problem. For example, Cu2+ is an essential trace element vital to the health of human beings. High intake of Cu2+ triggers aberrant oxidative damage and toxicity and causes serious health effects including diarrhea, stomach, liver damage, kidney disease and neurological diseases. ICP-MS and AAS/AES methods rely on large instruments, complicated analyte pre-treatment, and trained operator, making them not suitable for real-time environmental monitoring. Conventional chemical sensors with high sensitivity and selectivity usually require complicated synthesis of the active compounds, which is time-consuming and expensive. Here we demonstrate a new colorimetric sensor based on a stimuli-responsive hydrogel thin film interferometer. Its novel chemo-mechano-optical signal transduction significantly promotes the extraordinary sensing performance with ultra-high pM-level sensitivity and selectivity. The stimuli-responsive hydrogel thin films coated on reflective substrates show changes in their visually-detectable colors and shifts in their corresponding reflectance spectral peaks, as the consequence of film thickness changes in response to the analyte. When incorporated with specific ligands in the hydrogel, multiple ligands coordinate with one copper ion, leading to additional cross-linking of the hydrogel polymeric chains and subsequently the hydrogel film shrinking. With the decrease of hydrogel thickness, the interference spectral blue-shift could be read by spectrometer, as the color change observed by naked eyes. This unique chemo-mechano-optical signal transduction mechanism has significantly amplified the nm-scale hydrogel thickness change to a greater and more sensitive optical spectrum change. In addition, this novel sensing platform consisting of an ultra-thin film of a single responsive material is facile to fabricate and customize by directly incorporating different ligands during hydrogel film deposition for detecting a broad variety of chemical and biological molecules in air, wastewater or biofluids. Such capability of endowing desired sensibility by easily functionalizing a basic gel film opens up a new class of sensors with high versatility at low cost. Its ultra-fast 0.1~10-second-scale response also allows for real-time monitoring of metal pollutants in nature or waste water without heavy instrumentation.

Hydrogel interferometer naked-eye sensor for Cu2+ detection

256th National Meeting (2018)

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