Fe (III) ion modulated l-DOPA protected gold nanocluster probe for fluorescence turn on sensing of ascorbic acid

Abstract

The design of biocompatible fluorescent probes for targeting vital molecules in brain is highly desirable in recent years since various statistical studies conducted by World Health Organization point out the upcoming risk of neurodegenerative diseases like Alzheimer’s disease and Parkinson’s disease. In this circumstance, we synthesized water soluble fluorescent 3, 4-dihydroxy-l-phenyl alanine (l-DOPA) protected gold nanocluster (l-DOPA-AuNC) as l-DOPA can be effectively transmitted through blood-brain barrier. The as prepared l-DOPA-AuNCs exhibited fluorescence emission at 545nm. Interestingly, no obvious change in fluorescence emission of l-DOPA-AuNC was observed over a broad pH range (3 to 10), in various buffer solutions (10mM phosphate buffer), or in solutions with high ionic strength(2M KCl). However, the unique co-ordination of Fe(III) ions with catechol group on the surface of l-DOPA-AuNCs induce fluorescence quenching. Moreover, the fluorescence of l-DOPA-AuNCs can be regained completely by antioxidants (biological reducing agents) like Ascorbic Acid (AA) with high selectivity over other antioxidants, amino acids and neurotransmitters. The Limit of Detection (LOD) for Fe (III) ion and AA were found to be 25.5zM and 18.4pM respectively. Furthermore, human serum spiked with Fe (III) ions and AA is analyzed using this sensor and show good recovery percentage.