Colloids and Surfaces B: Biointerfaces 72 (2009) 68–74 Contents lists available at ScienceDirect Colloids and Surfaces B: Biointerfaces journal homepage: www.elsevier.com/locate/colsurfb Rapid screening of surfactant and biosurfactant surface cleaning performance Sagheer A. Onaizi a , Lizhong He b , Anton P.J. Middelberg a,b,∗ a Centre for Biomolecular Engineering, School of Engineering, The University of Queensland, St Lucia QLD 4072, Australia b Centre for Biomolecular Engineering, Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, St Lucia QLD 4072, Australia article info Article history: Received 28 November 2008 Received in revised form 12 February 2009 Accepted 23 March 2009 Available online 1 April 2009 Keywords: Biosurfactant Surfactant Surface plasmon resonance Cleaning Screening abstract Surface Plasmon Resonance (SPR) and rubisco protein stain were used as tools to screen the effec- tiveness of detergent formulations in cleaning a protein stain from solid surfaces. Surfactant and biosurfactant-based formulations, with and without added protease, were screened for cleaning per- formance. Enzyme-free detergent formulations at 1500ppm total surfactant were insufficient to cause complete surface cleaning, despite the high concentration of surfactant. The cleaning performance of a “home-made” formulation containing 2 ppm subtilisin A (SA) and 2 ppm sodium dodecyl benzyl sulphonate (SDOBS) was as efficient as the best amongst the three enzyme-free 1500 ppm formulations. The cleaning performance of 2 ppm SA in the absence of SDOBS was less effective than the combined formulation, even though 2 ppm SDOBS alone did not cause any protein removal. The observed synergis- tic performance was attributed to the cooperative mechanisms (chemical and physical attack) by which these two agents act on a rubisco stain. Replacing SDOBS in the enzyme-surfactant formulation with the same amount of surfactin biosurfactant (2ppm) gave the best rubisco removal of all formulations examined in this study, irrespective of the surface chemistry underlying the protein film. It was found that 75% and 80% of immobilised rubisco stain could be removed from hydrophobic and hydrophilic surfaces, respectively, by the biosurfactant-SA formulation (compared with 60% and 65%, respectively, using the SDOBS-SA formulation). Our results suggest that it may be possible to generate fully renewable biochemical-based cleaning formulations that have superior cleaning performance to existing technolo- gies. In developing optimised formulations, there is a pressing need for chip-based tools similar to that developed in this research. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Protein-fouled surfaces that require cleaning occur ubiquitously. For example, protein fouling on surfaces of food and process equip- ment, surgical and dental tools, fabrics, dishes, and contact lenses all present a challenge to cleaning technologies. Surface-bound protein stains can be removed, to different extents, by surfac- tants, enzymes, or surfactant-enzyme mixtures. The performance of cleaning agents differs according to the degree of the mutual interactions between the system components (solid surface, pro- tein, enzyme and surfactants). Understanding such differences might aid in optimising protein removal from solid surfaces, and hence it is necessary to screen and assess the performance of the cleaning agents on different stain-surface systems. Such screen- ing studies require relevant quantitative tools (e.g., a relevant model protein stain and suitable technique), as developed in this study. ∗ Corresponding author. Tel.: +61 7 3346 4189 fax: +61 7 3346 4197. E-mail address: a.middelberg@uq.edu.au (A.P.J. Middelberg). Rubisco is found in all photosynthetic leaves and represents up to 65% of the total soluble proteins in leaf extracts [1], mak- ing it a good representative of the class of grassy stains. It also forms a naturally tough stain since it irreversibly adsorbs at the air- liquid [2] as well as the solid–liquid interfaces. Rubisco has received little research attention and only few published studies have con- sidered it [3–6]. Kirchman et al. [3] studied the adsorption of rubisco from seawater on different surfaces and found that adsorp- tion increased as surface hydrophobicity increased. They pointed out that surface hydrophobicity controls adsorption in seawater, consistent with the phenomenon of charge screening in high-salt solutions. When the authors adsorbed rubisco from low saline buffer, they found no significant relationship between adsorption and surface hydrophobicity, and concluded that some other interac- tions, probably electrostatic, controlled protein-surface interaction. Electrostatic interactions can dominate protein-surface interac- tions when the surface and the protein are oppositely charged [7]. Taylor et al. [4] studied rubisco adsorption from seawater, at dif- ferent concentrations, on different surfaces. The authors reported that rubisco accumulation on solid surfaces is concentration depen- dent. At low concentrations, the protein exhibited higher affinity for hydrophobic surfaces, which is in agreement with the findings 0927-7765/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfb.2009.03.015