Abstract
The synthesis of ultra-small gold nanoclusters (Au NCs) with sizes down to 2 nm has received increasing interest due to their unique optical and electronic properties. Like many peptide-coated gold nanospheres synthesized before, modified gold nanoclusters with peptide conjugation are potentially significant in biomedical and catalytic fields. Here, we explore whether such small-sized gold nanoclusters can be conjugated with peptides also and characterize them using atomic force microscopy. Using a long and flexible elastin-like polypeptide (ELP)20 as the conjugated peptide, (ELP)20-Au NCs was successfully synthesized via a one-pot synthesis method. The unique optical and electronic properties of gold nanoclusters are still preserved, while a much larger size was obtained as expected due to the peptide conjugation. In addition, a short and rigid peptide (EAAAK)3 was conjugated to the gold nanoclusters. Their Yong’s modulus was characterized using atomic force microscopy (AFM). Moreover, the coated peptide on the nanoclusters was pulled using AFM-based single molecule-force spectroscopy (SMFS), showing expected properties as one of the first force spectroscopy experiments on peptide-coated nanoclusters. Our results pave the way for further modification of nanoclusters based on the conjugated peptides and show a new method to characterize these materials using AFM-SMFS.
Highlights
Gold nanoparticles, gold nanospheres [1–8] (Au NSs, size < 200 nm) and gold nanoclusters [9–17] (Au NCs, size < 2 nm), have received growing attention in recent years because of their excellent optical and electronic properties [18–20]
The Au-Cit NSs were synthesized by the classic method described above
The (ELP)20 -Au NSs were synthesized by the ligand-exchange method owing to the Au-S bond formation between cysteine residues in C-(ELP)[20] and Au-Cit NSs (Figure 1a)
Summary
Gold nanospheres [1–8] (Au NSs, size < 200 nm) and gold nanoclusters [9–17] (Au NCs, size < 2 nm), have received growing attention in recent years because of their excellent optical and electronic properties [18–20]. Many biomoleculeconjugated Au NSs have been prepared, such as peptide, protein, and DNA, which have a potential use in many biomedical and biosensing applications [21–29]. Most peptide-conjugated nanoparticles are prepared by using the larger size Au NSs, while the peptide-conjugation of ultra-small Au NCs is relatively less. Many protein-conjugated Au NSs have been prepared with more diverse and powerful applications [8,34–38], which are typically directly immobilized by non-specific interactions [39,40]. The conjugation of a lengthy peptide on Au NSs can be the first step toward site-specific protein modification. By conjugating a proper peptide with a recognition site for enzymatic connection, a target protein can be further coated on the nanoclusters via an enzymatic ligation with the peptide, such as using sortase or asparaginyl ligase (AEP) [41–43].
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