Chemical nanosensors based on molecularly-imprinted polymers doped with silver nanoparticles for the rapid detection of caffeine in wastewater

Highlights: • We describe novel molecularly-imprinted polymer (MIP) surface enhanced Raman scattering (SERS) nanosensors employing an integrated single-step detection. • Silver nanoparticles are introduced into the MIP material using precipitation polymerization. • The integrated approach greatly reduces the overall required analysis time versus conventional two-step processes by omitting the separate eluting step and subsequent addition of SERS substrates. • The proposed nanosensors rapidly detect caffeine as a pharmaceutical and personal care product pollutant. - Abstract: Caffeine is a common pharmaceutical and personal care product pollutant in wastewater. This work offers rapid and single-step detection of caffeine in an aquatic matrix based on high performance surface-enhanced Raman scattering (SERS). Novel chemical SERS nanosensors were developed employing molecularly-imprinted polymer (MIP) particles loaded with Ag nanoparticles (AgNPs) using precipitation polymerization to form AgNPs@MIP nanocomposites. Theophylline was applied as a dummy template molecule in the synthesis process due to its high structural similarity with caffeine and greater availability. The nanocomposite was characterized by Fourier transform infrared spectroscopy(FTIR), X-ray diffraction(XRD), and ultraviolet-visible (UV-vis) spectroscopy. Static and kinetic adsorption testing demonstrated the specific affinity of AgNPs@MIP nanocomposites for caffeine and a rapid adsorption equilibration rate. Moreover, a simple solid phase extraction cartridge comprising AgNPs@MIP nanocomposites as adsorbents (AgNPs@MISPE), a syringe, and a removable microporous membrane were employed to detect the SERS signal of caffeine. The AgNPs@MISPE was used to detect caffeine with excellent uniformity (relative standard deviation, RSD = 4.8%) and good repeatability (RSD = 8.7%). The separation and detection processes were integrated into a single step, and the overall analysis time was 23 min. The detection limit was 100 ng L^-1, which is less than the caffeine content reported in many rivers. The experimental results demonstrate that the proposed chemical nanosensors are a low-cost and reliable tool for the rapid screening of caffeine in wastewater or other aquatic matrices.