This ''Applications'' article focuses on superquenching of the fluorescence of conjugated polyelectrolytes and related fluorescent polyelectrolytes and its applications to biosensing. Superquenching can occur for both aqueous solutions of these polymers as well as for various supported formats. For biosensing the supported formats are generally most practical. Three practical sensing applications are reviewed: nucleic acids, protease enzyme activity assays and kinase/phosphatase assays based on metal-ion-mediated superquenching.

A charge neutral complex (CNC) was formed in aqueous solution by combining an orange light emitting anionic conjugated polyelectrolyte and a saturated cationic polyelectrolyte at a 1:1 ratio (per repeat unit). Photoluminescence (PL) from the CNC can be quenched by both the negatively charged dinitrophenol (DNP) derivative, (DNP-BS ؊ ), and positively charged methyl viologen (MV 2؉ ). Use of the CNC minimizes nonspecific interactions (which modify the PL) between conjugated polyelectrolytes and biopolymers. Quenching of the PL from the CNC by the DNP derivative and specific unquenching on addition of anti-DNP antibody (anti-DNP IgG) were observed. Thus, biosensing of the anti-DNP IgG was demonstrated.C onjugated polymers are a versatile class of organic materials that promise utility in a variety of applications ranging from antistatic coatings, electrodes, and transistors, to light-emitting diodes, large area displays, photodetectors, photovoltaic cells, and lasers (1-3). The electrical, optical, and electrochemical properties of conjugated polymers can be modified by chemical synthesis and are strongly affected by relatively small perturbations, including changes in temperature, solvent, or chemical environment. As a result of this sensitivity, conjugated polymers are promising as sensory materials (4, 5); sensing may be accomplished by transducing and͞or amplifying physical or chemical changes into electrical, optical, or electrochemical signals. Conjugated polymers have been used to detect chemical species (chemosensors) (6), such as ions (7-11), gases (for example, trinitrotoluene) (6,(12)(13)(14), and other chemicals (15), or biomolecules such as proteins, antibodies (16-27), and DNA (28-31), using electrical (13, 15), chromic (7, 8, 16-19), electrochemical (7-9, 20-25, 28-31), photoluminescent (11, 26), chemoluminescent (27), or gravimetric (14) responses.Contemporary biosensor and bioassay developments have focused on mimicking natural host-receptor (''lock-and-key'') interactions. ''Lock-and-key'' molecular recognition can be between enzyme and substrate, ligand and receptor, antibody and antigen, or between two strands of nucleic acids with complementary sequences. Although antibody-based ELISAs are widely used for detection of biological species with high sensitivity, these assays are relatively labor-intensive and timeconsuming (hours to days) and require two different antibodies of defined specificities to adequately detect the target molecule (potentially making them cumbersome to perform) (32). Additionally, the detection of small molecules using ELISA can seldom be accomplished because of the recognition of one epitope by both capture and detection antibodies. Therefore, competition assays have to be performed that are both less accurate and more time consuming.Biosensors based on conjugated polymers as sensory materials exhibit real-time response [electrochemical (20-25) or optical (16-19, 26)] to the ligand-receptor recognition event. The coupling of a recognition event to photoinduced electron...

Herein we describe studies that indicate a cationic conjugated polyelectrolyte shows biocidal activity against gram-negative bacteria (Escherichia coli, E. coli, BL21, with plasmids for Azurin and ampicillin resistance) and gram-positive bacterial spores (Bacillus anthracis, Sterne, B. anthracis, Sterne). These studies were carried out with aqueous suspensions of the conjugated polyelectrolyte, with the polyelectrolyte in supported formats and with samples in which the conjugated polyelectrolyte was coated on the bacteria. The results are interesting in that the biocidal activity is light-induced and appears effective due to the ability of the conjugated polyelectrolyte to form a surface coating on both types of bacteria. The effects observed here should be general and suggest that a range of conjugated polyelectrolytes in different formulations may provide a useful new class of biocides for both dark and light-activated applications.

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