A novel superparamagnetic photonic crystal DNA probe (Fe(3)O(4)@SiO(2)@amino@DNA SPC) was developed to enable rapid visual detection of Hg^(2+). This unique photonic crystal (PC) was synthesized by combining superparamagnetic nanospheres with DNA probes. The DNA probe, rich in thymine (T), detects mercury ions through base mismatch, resulting in the formation of T-Hg^(2+)-T loop hairpin structures. With the binding of Hg^(2+) to the probe attached to superparamagnetic nanospheres, the …