An increasing number of biotechnology applications are realised with the help of gold nanoparticles.
These can be visualised permanently (without bleaching) in both light and electron microscopy.
In addition, gold is known to be bio-inert – an important aspect in many biological and medical applications.
This can be taken advantage of by a conjugation to biomolecules, enabled by the chemical affinity of
gold to thiol groups:
such as peptides, oligonucleotides, or antibodies, can be attached to gold surfaces by using covalent thiol bonding with or without spacer molecules. In any case, the gold surface must be accessible to the molecules directly or by means of ligand exchange (replacing surface ligands that are already present on the surface by molecules of higher affinity). The obvious advantage of ligand-free nano-gold or significantly lower ligand coverage is that molecules attach to a free gold surface most efficiently.
Gold nanoparticles with the lowest possible ligand coverage are available by laser ablation at the moment of their generation. Using hybrid process chambers that combine laser ablation and conjugation, clean nano-gold can be conjugated with functional molecules with highest efficiency. Such conjugates can be used in all nano-gold applications that have been demonstrated in biotech research.
Compared to chemically synthesized materials, laser-generated conjugates excel by their higher
Reactivity and lower toxicity, opening up a wider window for applications.
Their surface coverage with bio-functional ligands is up to 5 times higher than that of chemically synthesized nano-gold
In case of antibodies, DNA, or aptamers, applications benefit especially from the high specificity,
caused by the higher ligand grafting density.
The use of an aptamer directed against a prostate-specific membrane antigen (PSMA) for gold
nanoparticle functionalization led to the same conclusion that conjugation efficiency is higher if the aptamers are bound to ligand-free gold nanoparticles.
This is especially relevant, as in the case of aptamers, the high conjugation yield saves very precious material. During functionality testing, the ligand-covered gold conjugates were found to strain prostate cancer tissue as efficiently as conventional fluorophore-labelled probes, compared to a negative control
Conjugating ligand-free gold nanoparticles with a short cell-penetrating peptide (CPP) allows the rapid
design of cell-penetrating nanomarkers for intracellular bio-imaging.
Since CPPs are typically cationic at neutral pH and highly charged, buffering pH at appropriate values during conjugation is important.
Significantly enhanced penetratin conjugation efficiencies could be observed at higher pH values. This effect could be attributed to a higher extent of specific dative binding of the penetratin’s sulfide to the gold nanoparticle surface at increased pH.
A simple biological by study revealed a successful uptake of gold-penetratin bioconjugates: within 2 hours, up to 100 % of coincubated cells were loaded with
penetratin-conjugated gold nanoparticles