Abstract
In this study, we established a new fluorescent indicator platform. The responsive element consists of poly(N-isopropylacrylamide) nanospheres that include small percentages of fluorescein and a ligand, anilinodiacetate (phenylIDA). Nanosphere diameters were determined to be in the range from 50 to 90 nm by scanning electron microscopy. They were entrapped in a polyacrylamide gel to prevent nanosphere aggregation. At pH 6, the ligand is negatively charged in the absence of metal ions. Charge-charge repulsion causes the nanosphere to swell. Dynamic light scattering measurements show that these nanospheres do not shrink and aggregate at high temperature. Cu(II) binding neutralizes the charge causing the particles to shrink. This brings fluoresceins closer together, increasing the degree of self-quenching. The intensity decreases by 30% as Cu(II) concentration increases. To rule out the possibility that the observed decrease in intensity was due to Cu(II) quenching of fluorescence, we also added Zn(II) and observed a decrease in intensity. This approach can be adapted to sense different metal ions and different concentrations of Cu(II) by changing the ligand.
Highlights
Cu(II) is an active producer of oxidative stress for both plants [1,2,3] and animals [4]
The PA gel formed with self-quenching pNIPAM nanoparticles was immersed in DI water and rinsed several times in order to remove particles that are not immobilized in the gel
The surface of the particles is not that smooth, and there is some deformation in shape
Summary
Cu(II) is an active producer of oxidative stress for both plants [1,2,3] and animals [4]. Several studies report ligands that change fluorescence when they bind Cu(II) These can potentially be used to measure bioavailable Cu(II). WeWe prefer to base on metal induced changes in a water-soluble polymer conformation conformation detected via fluorescence. This metal ions neutralizes theneutralizes negative charge causing the nanoparticle to shrink This results in a results in a change in fluorescein concentration per unit volume. The approach is general because binding of other metal ions will change the charge on the polymer backbone leading to swelling or shrinking depending on whether the charge increases or decreases. The indicator platform we demonstrate is applicable other metal ions the particular ligand ofthat is. Metal ions will the charge on the polymer backbone leading to swelling or shrinking depending on whether the charge increases or decreases.
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