Fluorescence assay of Fe (III) in human serum samples based on pH dependent silver nanoclusters

- Silver nanoclusters based assay for Fe (III) was reported.
- Fluorescence intensity of silver nanoclusters was pH dependent and pH reversible.
- Sensitive assay of Fe (III) was achieved through pH adjustment of silver nanoclusters.
- The sensitivity was about 50 times higher than traditional method.
- The assay was successfully applied for detection of Fe (III) in human serum samples.

Silver nanoclusters (Ag NCs) were synthesized based on dC12 strands as template. The fluorescence intensity of the Ag NCs was found to be pH dependent and pH reversible, that is, the fluorescence intensity was quenched with the decrease of pH and can be recovered to exact value again with the adjustment of pH value to neutral. This pH dependent fluorescence property was utilized for the sensitive detection of Fe (III). With the addition of acid Fe (III) solution to decrease the pH value of Ag NCs and then corresponding amount of alkali to adjust the pH to neutral, the fluorescence intensity of Ag NCs was found to be still quenched in contrary to that without Fe (III). Compared to the direct addition of Fe (III) into Ag NCs, this method utilizing pH adjustment resulted in around 50 times of sensitivity enhancement for Fe (III) detection. At the optimal pH of 4, linear relationship was obtained between fluorescence change and logarithm of Fe (III) concentration in the range from 0.01 to 1 μM with the detection limit of 3 nM. Recovery test was also performed for the detection of Fe (III) in human serum samples with good results.