We present a new platform for visual and spectroscopic detection of bacteria. The detection scheme is based on the interaction of membrane-active compounds secreted by bacteria with agar-embedded nanoparticles comprising phospholipids and the chromatic polymer polydiacetylene (PDA). We demonstrate that PDA undergoes dramatic visible blue-to-red transformations together with an intense fluorescence emission that are induced by molecules released by multiplying bacteria. The chromatic transitions are easily identified by the naked eye and can also be recorded by conventional high-throughput screening instruments. Furthermore, the color and fluorescence changes generally occur in shorter times than the visual appearance of bacterial colonies on the agar. The chromatic technology is generic and simple, does not require identification a priori of specific bacterial recognition elements, and can be applied for detection of both gram-negative and grampositive bacteria. We demonstrate applications of the new platform for reporting on bacterial contaminations in foods and for screening for bacterial antibiotic resistance.The emerging global risks of bioterrorism, the recurring incidents of bacterial food contaminations, and the need to monitor sterile environments in health care applications and other industries have pushed the development of methods for detection of pathogens to the forefront of technological and scientific research. Numerous technologies for reporting on bacterial presence have been developed (3,5,9,25,26). There are, however, limitations to existing bacterial detection techniques as rapid and generic approaches. Specifically, many bioanalytical techniques employed for pathogen detection (such as culture-based methods) provide results after relatively long time spans (several hours to days) (10). Other currently employed technologies often involve complex detection mechanisms that require specialized instrumentation, application by trained personnel, and the need for active operation (addition of reagents, initiation of chemical reactions, etc.), which overall do not lend their use in settings other than laboratory environments (3, 6). Furthermore, a prerequisite for many detection methods is the detailed understanding of the biochemical and structural properties of the bacterial species sought, limiting applications in the case of unknown pathogens or variants (9, 31).Various membrane-active compounds are released by bacteria to their environments (2, 30), a process that often has an essential functional role as a means for overcoming host defense mechanisms, allowing colony proliferation, and facilitating bacterial communication (17). Membrane-active peptides and toxins, in particular, are produced by bacteria, for example, pneumolysins secreted by streptococci (27) and ␣-toxin, which is the major cytolysin emitted by Staphylococcus aureus (1). Secretion of pore-forming exotoxins by bacteria is abundant, and endotoxins, such as lipopolysaccharides, which are often released by gram-negative bacteria, ...

Glass-supported films of lipids and polydiacetylene were applied for visual detection and colorimetric fingerprinting of bacteria. The sensor films comprise polydiacetylene domains serving as the chromatic reporter interspersed within lipid monolayers that function as a biomimetic membrane platform. The detection schemes are based on either visible blue-red transitions or fluorescence transformations of polydiacetylene, induced by amphiphilic molecules secreted by proliferating bacteria. An important feature of the new film platform is the feasibility of either naked-eye detection of bacteria or color analysis using conventional scanners. Furthermore, we find that the degrees of bacterially induced color transformations depend both on the bacterial strains examined and the lipid compositions of the films. Accordingly, bacterial fingerprinting can be achieved through pattern recognition obtained by recording the chromatic transformations in an array of lipid/PDA films having different lipid components.

Aim:  Development of a new chromatic (colorimetric/fluorescence) bacterial sensor, for rapid, sensitive and versatile detection of bacterial proliferation. Methods and Results:  We constructed agarose‐embedded chromatic films which produce dramatic colour changes and fluorescence transformations in response to bacterial growth. The sensing constructs comprise glass‐supported Langmuir–Schaeffer phospholipid/polydiacetylene films that undergo both blue‐red transformations and induction of intense fluorescence following interactions with bacterially secreted amphiphilic compounds that diffuse through the agarose. The agarose matrix coating the sensor film further contains growth nutrients, facilitating signal amplification through promotion of bacterial culture proliferation. The agarose layer also constitutes an effective barrier for reducing background signals not associated with the bacteria. We demonstrate the applications of the new sensor for the detection of Gram‐negative and Gram‐positive bacteria, and for screening specimens of physiological fluids (blood and urine) and foods (meat) for bacterial contaminations. Conclusions:  The experiments demonstrate that the new agarose‐embedded film constructs are capable of bacterial detection through visible colour transitions and fluorescence emission recorded in conventional apparatuses. Significance and Impact of the Study:  This work demonstrated a new simple chromatic platform for bacterial detection, based on the generation of easily recorded colour and fluorescence changes. The new bacterial detection scheme is highly generic and could be employed for varied practical uses, in which, rapid reporting on bacterial presence is required.

This short review focuses on recent innovative systems and experimental approaches designed to investigate membrane processes and biomolecular interactions associated with membranes. Our emphasis is on "biomimetics" which reflects the significance and contributions of the chemistry/biology interface in addressing complex biological questions. We have not limited this review to discussion of new "sensors" or "assays"per se, but rather we tried to review new concepts employed for analysis of membrane processes.

Inducing insulin actions by intracellular PIP3 delivery (PEI-25/PIP3 complexes) in some forms of insulin-resistant cells provides the first proof-of-principle for the potential therapeutic use of PIP3 in a "second-messenger agonist" approach. In addition, utilization of an artificial bio-mimetic membrane platform to screen for highly efficient PIP3 delivery predicts biological function in cells.