Colloidal silver (a colloid consisting of silver particles suspended in liquid) and formulations containing silver salts were used by physicians in the early 20th century, but their use was largely discontinued in the 1940s following the development of safer and effective modern antibiotics.
With increased bacteria resistance against antibiotics the world is looking for alternatives. Before antibiotics colloidal silver was used (mainly for wound dressings and such); a revisit of colloidal silver.
It needs to be said that colloidal silver can have potentially irreversible side effects like argyria.
From: (2008) Colloidal silver solutions with antimicrobial properties1
The presented method allows obtaining of some stable colloidal solutions containing up to 35 ppm of Ag with very good antimicrobial and anti-fungal properties.
From: (2006) Bacterial silver resistance: molecular biology and uses and misuses of silver compounds2
Paradoxically, higher levels of Cl− bring the silver back into solution as a ‘bioavailable’ anion, AgCl2−, increasing the Ag(I) sensitivity of sensitive bacteria while making the difference between susceptibility levels for sensitive and for resistant bacteria greater .
From: (2010) Bactericidal effect of silver nanoparticles against multidrug-resistant bacteria3
Our data suggest that silver nano particles are effective broad-spectrum biocides against a variety of drug-resistant bacteria, which makes them a potential candidate for use in pharmaceutical products and medical devices that may help to prevent the transmission of drug-resistant pathogens in different clinical environments.
A quick glance seems that nano particles is a more 'attractive' term then colloidal silver and perhaps there is evidence that the size and shape of the particle can be better controlled in this way to be more effective.
A few other papers talk about combining silver with other particles to increase the sensitivity or susceptibility of bacteria to Ag making it more effective.