Former PhD student of Prof Paunov Josef graduated as PhD in 2013 and after a brief post-doc period at Leeds University, Encapsulation Scientist at Ashland Inc (Bradford), he is currently working as a Research Associate in RB (Hull). PhD Supervisor: Prof. Vesselin Paunov (PI)

Research project 1 (PhD thesis):

Colloid Antibodies for Shape Recognition and Killing of Microorganisms

We developed a class of selective antimicrobial agents based on the recognition of the shape and size of the bacterial cells. These agents are anisotropic colloid particles fabricated as negative replicas of the target cells which involve templating of the cells with shells of inert material followed by their fragmentation [1-2]. The cell shape recognition by such shell fragments is due to the increased area of surface con-tact between the cells and their matching shell fragments which resembles antibody-antigen interaction. We produced such “colloid antibodies” with photothermal mechanism for shape-selective killing of matching cells (see Fig. 1). This was achieved by the subsequent deposition of: (i) gold nanoparticles and (ii) silica shell over yeast cells, which were chosen as model pathogens. We demonstrated that fragments of these composite gold nanoparticle/silica shells act as “colloid antibodies” and can bind to yeast cells of the same shape and size and deliver gold nanoparticles directly onto their surface. We showed that after laser irradiation, the localized heating around the gold nanoparticles kills the microbial cells of matching shape. We confirmed the cell shape-specific killing by photothermal colloid antibodies in a mixture of two bacterial cultures of different cell shape and size (see Fig. 2). This approach opens a number of avenues for building powerful selective biocides based on combinations of colloid antibodies and cell killing strategies which can be applied in new antibacterial therapies.

Fig. 1 (A) Fabrication of the photothermal colloid antibodies by templating AuNP-coated cells with silica and subsequent silica shell fragmentation and bleaching of the cell templates with Piranha solution. (B) Experimental set up illustrating the principle of action of photothermal colloid antibodies (PCA) with integrated AuNPs on their inner surface in a suspension of two types of microbial cells of different morphology. PCA recognizes and bind only to bacteria of matching shape which are killed selectively by photothermal effect after laser irradiation while the other bacteria in the mixture remain viable. Grey color signifies dead cells.

Fig.2. A graphical summary of the selective yeast cell recognition and killing experiments by PCA in a mixture of yeast and B. subtilis. Error bars represent the standard deviation.

References

1. Borovicka, J., Stoyanov, S.D., Paunov, V.N., Shape recognition of microbial cells by colloidal cell imprints, Nanoscale, 57 (2013) 8560 – 8568.
2. Borovicka, J., Metheringham, J., Madden, L.A., Walton C.D., Stoyanov, S.D., Paunov, V.N., “Photothermal colloid antibodies for shape-selective recognition and killing of microorganisms.”, J. Am. Chem. Soc., 135 (2013), 5282-5285. [Highlighted by ACS Press]