Many environmental pollutants are prevalent in water solution and can have severe negative impacts on human health and the ecosystem. Therefore, rapid in situ detection is important, whereas current methods rely on time-consuming sample transportation, pretreatment, and physical separations prior to detection. Techniques such as UV-vis absorbance and fluorescence spectroscopy allow for an inexpensive, simple, and portable means to obtain data immediately after sample collection. However, sensors providing optical signals at the low analyte concentrations required for environmental and biological applications run into a major challenge with this approach, especially in complex environments such as seawater, whose components often attenuate the desired optical signals. To overcome these hurdles, highly fluorescent fluorene-based conjugated polymers were developed and used as effective sensors for divalent metal cations and organic azo dye analytes in seawater conditions. These polymers contain a common fluorene core separated by a variety of conjugated spacer groups. Pendant arms were also covalently attached to the sp3 carbon of the fluorene monomer, allowing for strong binding or to promote fluorescence modulation though physical means such as the inner filter effect (IFE). Taken together, these structural modifications can cause a significant change in the optical signature and response of the polymers, with minimal interference from contaminants found in more complex aqueous environments, e.g. seawater. Compared to small-molecule fluorophores, conjugated polymers provide much greater sensitivity thanks to π-mediated signal amplification along the backbone of the polymer. This signal enhancement has led to their successful use in high-salinity environments using well-established pattern recognition methods for data processing, to recover selectivity for the detection of many similar and environmentally relevant analytes using a minimal number of polymeric receptors. These combined effects allowed us to achieve detection of important pollutants and contaminants with part-per-trillion sensitivity even in highly interfering aqueous environments, without costly and time-consuming physical separations. As we continue to study the properties of these polymers, we aim to achieve improved resolution and quali-quantitative differentiation of trace analytes in environmental and biological samples using straightforward, high throughput, and portable instrumentation.

Conjugated polymers as versatile optical sensors for pollutants in complex and high-salinity media, including seawater

ACS Spring Meeting 2021

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