The finding of giant magnetoresistive（GMR） effect develops a new field for the sensing application with magnetic nanoparticles（MNPs） labeling. A convenient GMR sensor was built with a permanent magnet to excite the MNPs in this work. The sensing element contained a Wheatstone bridge with the GMR material as one of its branches. The magnetic field from MNPs unbalanced the Wheatstone bridge. After being amplified, the output signals were recorded. The construction and optimization of the magnetoresistive sensing platform were discussed in detail. The detection of three kinds of MNPs validated the performance of the proposed GMR sensor. The sensor showed a fast response to the addition or removal of MNPs. Because of its simplicity, this kind of GMR sensor can be developed in a routine laboratory. The finding of this new GMR sensor will promote the development of the method of probing biomoleeules and the study on the biomolecular interaction after being labeled magnetically.
Mn-doped ZnS quantum dots/methyl violet nanohybrids were explored to develop a novel room temperature phosphorescence (RTP) sensor for the detection of DNA. Methyl violet (MV) as the electron acceptors was adsorbed on the surface of the quantum dots (QDs) to quench the RTP of the Mn-doped ZnS QDs through an electron-transfer process under excitation. The addition of DNA recovered the RTP signal of the Mn-doped ZnS QDs due to the binding of MV with DNA and the removal of MV from the surface of the Mn-doped ZnS QDs. Under the optimal conditions, the enhanced RTP intensity of the Mn-doped ZnS QDs/MV nanohybrids linearly increased with the concentration of DNA from 0.08 to 12 mg L-1 with the detection limit of 33.6 μg L-1. The relative standard deviation for eleven replicate detections of the reagent blank was 3.7%. The developed method was applied to the detection of DNA in spiked urine samples with recoveries of 96%-103% without interference from nonspecific fluorescence.
