Near-infrared fluorescent ribonuclease-A-encapsulated gold nanoclusters: preparation, characterization, cancer targeting and imaging

Abstract

Ultra-small gold nanoclusters (AuNCs) have unique size-dependent optical, electrical and chemical properties. They have emerged as a new nanomaterial with broad applications in optoelectronics, catalysis, biosensing, and bioimaging. Several strategies have been exploited to prepare AuNCs of different "magic number" sizes, using different templates e.g. dendrimers, polyethyleneimines, peptides, and more recently, proteins. Notwithstanding, almost all bio-template-protected AuNCs reported so far exhibit fairly low fluorescence quantum yields (QYs), typically <5%, which is especially true for AuNCs prepared using the protein templates. In this paper, we report a facile, one-pot aqueous synthesis of highly fluorescent AuNCs using bovine pancreatic ribonuclease A (RNase-A) as the bio-template. The as-prepared AuNCs not only fluoresce strongly at the near-infrared (NIR) region (λ(em) = 682 nm), but also exhibit an elevated QY of ∼12%. Additionally, the RNase-A-encapsulated AuNC (RNase-A-AuNC) displays an exceptionally large Stokes shift of ∼210 nm as well as a single dominant fluorescence lifetime of ∼1.5 μs, about three orders of magnitude longer than biological autofluorescence. Furthermore, by coupling vitamin B(12) (VB(12)) to the RNase-A-AuNC, we develop a multifunctional nanoplatform that is suitable for simultaneous targeting and imaging of cancer at the cellular level using Caco-2 cell lines as an in vitro model. Since VB(12) has effective uptake pathways in the digestive system, this nanoplatform may have potential for targeted oral drug delivery in vivo.

Protein stabilized Au nanoclusters: spectral properties and photostability

“…Currently, considerable research efforts are directed towards investigation of Au NCs synthesis [4][5][6][7][8][9][10], structure [7,11,12], optical properties [4,[13][14][15][16], photostability [17][18][19][20][21] and possible applications for material sensing [5,[22][23][24] as fluorescence [25,26] and dual-modality imaging contrast agents [27,28]. However, colloidal stability, photostability, dependence of optical properties on temperature, interaction of BSA-Au NCs with biomolecules are still poorly investigated.…”

Synthesis of water-soluble gold clusters in nanosomes displaying robust photoluminescence with very large Stokes shift

“…Shichibu et al [12] observed that Au 13 clusters obtained by treating a polydisperse sample with hydrochloric acid show an emission band at 766 nm by excitation at 360 nm. Shibu et al [13] prepared Au 15 trapped in cyclodextrins showing the maximum emission centered at 690 nm when excited at 375 nm. Biang et al [14] synthesized luminescent Au clusters with a bright red emission and large Stokes shift using both histidine and 11-mercaptoundecanoic acid as stabilizers.…”

“…Biang et al [14] synthesized luminescent Au clusters with a bright red emission and large Stokes shift using both histidine and 11-mercaptoundecanoic acid as stabilizers. Gold clusters were also obtained using ribonuclease A as bio-template showing a large Stokes shift (210 nm) and a high luminescence quantum yield (QY) of 12%, being suitable for cancer targeting and imaging [15]. In the described cases the authors did not investigate the reasons for the observed luminescence.…”

Fluorescent Gold Nanoclusters: Promising Fluorescent Probes for Sensors and Bioimaging

“…Tseng's group presented a novel approach for preparing highly fluorescent Au 8 NCs and Au 25 NCs by using lysozyme type VI (Lys VI) at pH 3 and pH 12, [43] respectively [49]. Inspired by this finding, researchers try to explore other proteins as efficient bioscaffolds for synthesizing AuNCs such as insulin [50], transferrin-family proteins [51,52], horseradish peroxidase [53], pepsin [54], denatured BSA [55], ribonuclease A [56], trypsin [57], DNase I [58], ovalbumin [59], and egg white [60].…”