Novel blue-emitting gold nanoclusters confined in human hemoglobin, and their use as fluorescent probes for copper(II) and histidine

Abstract

We report on the synthesis and characterization of highly fluorescent gold nanoclusters (Au-NCs) from a gold precursor using a single-step chemical reduction in the presence of human adult hemoglobin (Hb). The conformational changes of Hb before and after cluster formation were studied by various spectroscopic techniques. The Au-NCs in Hb display blue fluorescence with a peak centered at 450 nm (photoexcited at 365 nm) and a quantum yield of 2.8 %. The Au-NCs exhibit excellent photostability and long-term stability, and can be applied in the pH range 5-12 even in the presence of high electrolyte concentrations. The Au-NCs in Hb can act as a highly sensitive and selective fluorescent turnoff probe for Cu(II) ion. The observed reversible fluorescence recovery of Hb-AuNCs/Cu(II) aggregates was exploited to develop a selective and sensitive turn-on fluorescence assay for His. Under optimized conditions, the probe gives a fluorescent response that is linear in the 0.1 to 20.0 μM concentration range of Cu(II), with a limit of detection of 28 nM. The probe for His, in turn, has a linear range in the 1-21 μM concentration range, and the limit of detection is 0.6 μM.

Determination of the activity of hydrogen peroxide scavenging by using blue-emitting glucose oxidase–stabilized gold nanoclusters as fluorescent nanoprobes and a Fenton reaction that induces fluorescence quenching

“…Although protein-directed fluorescent AuNCs with red emission were frequently reported, the synthesis of other color fluorescent AuNCs with proteins-directed approach was very rare [24,29]. We observed that Fenton reaction can induce a significant fluorescence quenching of the prepared AuNCs.…”

A novel electrochemical hydrogen peroxide biosensor based on hemoglobin capped gold nanoclusters–chitosan composite

“…2B). 20,26 ( Fig. 2B that the Soret band of Hb alone (curve a) is located at about 412 nm, but in the presence of AuNCs (curve b), it is shifted to 403 nm while its intensityis significantly decreased.…”

“…20,21 In brief, a 5 mL aqueous solution of HAuCl 4 (2.8 mM, 37 °C) was reacted with 5 mL of human adult hemoglobin (Hb) (7 mg mL -1 , 37 °C), under vigorous stirring. The generation of blue emitting Hb-AuNCs was mainly based on previously established synthetic methods.…”

“…Fig. 20 Moreover, the 1436 cm −1 band is due to the vibration of tryptophan (Trp) that becomes drastically larger when nanoclusters are prepared at high pH. Compared with the pure IR spectra of Hb (a), the intensity of amide I (1650 cm −1 ) of Hb immobilized on Hb-AuNCs (b) is decreased, and amide II (1533 cm −1 ) is disappeared, in the expense of the appearance of a rather sharp band at 1436 cm −1 (Fig 2A).…”

“…25 The UV-visabsorption spectroscopy was then employed for the conformation study of Hb in composite film (Fig. 20 In addition, the increase in intensity of a bandaround 215 nm (related to the α-helix structure of the protein) and the disappearance of bands located at 280 nm (due to the phenyl group of Trp and tyrosine residues), and 540 and 575 nm (related to oxy-band or Q-band) confirm that the microenvironment surrounding heme in Hb-AuNCs is different from that of native Hb. It is quite obvious from Fig.…”