A hydrogel microsphere-based sensor for dual and highly selective detection of Al³⁺ and Hg²⁺

Traditional fluorescent sensors for simultaneous detection of metal ions require the use of specially designed fluorescent probes. In this manuscript, we have employed a new strategy for the design of a sensor for simultaneous detection of metal ions that is based on a fluorescent probe encapsulated hydrogel matrix. An investigation designed to assess this strategy led to the development of a novel dual fluorescent encapsulated hydrogel microsphere sensor for sensitive and simultaneous detection of Al³⁺ and Hg²⁺. The hyperbranched poly (poly (ethylene glycol) diacrylate) (HB-PEGDA) and thiolated sodium alginate (SA-SH) composite hydrogel microspheres used to construct the sensor, which contain two fluorescent probes encapsulated in a highly dense manner, were prepared by using a self-assembly method in conjunction with a microfluidic device. The functionalized hydrogel microspheres were shown to exhibit high selectivity for Al³⁺ and Hg²⁺ among various metal ions with a detection limit of 70 nM and 120 nM, respectively. In addition, the hydrogel microspheres can be readily separated from test samples and utilized for repeated use by removing Al³⁺ and Hg²⁺ by addition of a solution containing EDTA and KI. Compared with previously devised sensors, the new HB-PEGDA/SA-SH composite hydrogel microspheres containing two encapsulated fluorescent probes are readily prepared and effective for simultaneous detection of two different metal ions.