As inspired by the Dot blot analysis, a well known technique in molecular biology and genetics for detecting biomolecules, a new paper-based platform for colorimetric detection of specific DNA sequences employing peptide nucleic acid (PNA) as a probe has been developed. In this particular study, a pyrrolidinyl PNA bearing a conformationally rigid d-prolyl-2-aminocyclopentanecarboxylic acid backbone (acpcPNA) was used as a probe. The filter paper was modified to be positively charged with grafted polymer brushes of quaternized poly(dimethylamino)ethyl methacrylate (QPDMAEMA) prepared by surface-initiated polymerization of 2-(dimethylamino)ethyl methacrylate from the filter paper via ARGET ATRP followed by quaternization with methyl iodide. Following the Dot blot format, a DNA target was first immobilized via electrostatic interactions between the positive charges of the QPDMAEMA brushes and negative charges of the phosphate backbone of DNA. Upon hybridization with the biotinylated pyrrolidinyl peptide nucleic acid (b-PNA) probe, the immobilized DNA can be detected by naked eye observation of the yellow product generated by the enzymatic reaction employing HRP-labeled streptavidin. It has been demonstrated that this newly developed assay was capable of discriminating between complementary and single base mismatch targets at a detection limit of at least 10 fmol. In addition, the QPDMAEMA-grafted filter paper exhibited a superior performance to the commercial membranes, namely Nylon 66 and nitrocellulose.

This research focuses on the synthesis of ZnO quantum dots with a cationic polymer coating consisting of poly[2-(methacryloyloxy)ethyl]-ammonium chloride-co-poly(poly-ethyleneglycol methyl methacrylate (p(METAC-PEOMEMA)) for Fe 2 + detection. The copolymers of p(METAC-PEOMEMA) at various molar ratios of METAC/PEOMEMA (100/0, 38/62, and 9/91) were synthesized by RAFT polymerization. The p(METAC-PEOMEMA) capped trisodium citrate-ZnO quantum dot (p(METAC-PEOMEMA)-ZnO QDs) were prepared via ionic interaction of trisodium citrate-ZnO QDs and p(METAC-PEOMEMA). The optical properties of the polymer-capped ZnO QDs were studied by UV-Vis and fluororescence spectrophotometry. The p(METAC-PEOMEMA)-ZnO QDs exhibited excellent properties such as high monodispersity in particle sizes, good stability, excellent water dispersibility, and good quantum yield of 27-32%. The p (METAC 9 -PEOMEMA 91 )-ZnO QDs is quenched by Fe 2 + with a good selectivity over other metal ions such as Fe 3 + , Hg 2 + , Co 2 + , Pb 2 + , Cd 2 + , Ni 2 + , Ag + , Cu 2 + , and Na + . A good linear relationship between relative fluorescence intensity and the concentration of Fe 2 + ion was observed over an Fe 2 + concentration range from 0.47 μM to 5.6 μM, with a limit of detection and limit of quantitation at 0.34 μM and 0.51 μM, respectively. Its application for the detection of Fe 2 + ion in drinking water samples was demonstrated.[a] Dr.