Cationic liposomes for generic signal amplification strategies in bioassays

Abstract

Liposomes have been widely applied in bioanalytical assays. Most liposomes used bare negative charges to prevent non-specific binding and increase colloidal stability. Here, in contrast, highly stable, positively charged liposomes entrapping the fluorescent dye sulforhodamine B (SRB) were developed to serve as a secondary, non-specific label‚ and signal amplification tool in bioanalytical systems by exploiting their electrostatic interaction with negatively charged vesicles, surfaces, and microorganisms. The cationic liposomes were optimized for long-term stability (> 5 months) and high dye entrapment yield. Their capability as secondary, non-specific labels was first successfully proven through electrostatic interactions of cationic and anionic liposomes using dynamic light scattering, and then in a bioassay with fluorescence detection leading to an enhancement factor of 8.5 without any additional surface blocking steps. Moreover, the cationic liposomes bound efficiently to anionic magnetic beads were stable throughout magnetic separation procedures and could hence serve directly as labels in magnetic separation and purification strategies. Finally, the electrostatic interaction was exploited for the direct, simple, non-specific labeling of gram-negative bacteria. Isolated Escherichia coli cells were chosen as models and direct detection was demonstrated via fluorescent and chemiluminescent liposomes. Thus, these cationic liposomes can be used as generic labels for the development of ultrasensitive bioassays based on electrostatic interaction without the need for additional expensive recognition units like antibodies, where desired specificity is already afforded through other strategies.

Liposome-Based Bioassays

“…Finally, it is worth noting that negatively charged vesicles and micro-organisms can be labelled, via simple electrostatic interaction, with cationic liposomes. This approach has been recently applied for the labeling of Gram-negative bacteria [ 95 ].…”

Liposomes as Carriers of GHK-Cu Tripeptide for Cosmetic Application

“…An additional advantage of these phospholipid vesicles is the possibility of the structural modification of their membranes using sterols [26], polymers [27], proteins [28] or sugars [29]. The liposomal systems can be prepared by various methods, including thin-film hydration [30], microfluidics [31], reverse phase evaporation [32] and ethanol injection [33].…”