Use of the CNC minimizes nonspecific interactions (which modify the PL) between conjugated polyelectrolytes and biopolymers

Use of the CNC minimizes nonspecific interactions (which modify the PL) between conjugated polyelectrolytes and biopolymers. 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 (1C3). 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 and/or 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 (7C11), gases (for example, trinitrotoluene) (6, 12C14), and other chemicals (15), or biomolecules such as proteins, antibodies (16C27), and DNA (28C31), using electrical (13, 15), chromic (7, 8, 16C19), electrochemical (7C9, 20C25, 28C31), photoluminescent (11, 26), chemoluminescent (27), or gravimetric (14) responses. Contemporary biosensor and bioassay developments have focused on mimicking natural hostCreceptor (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 time-consuming (hours cIAP1 Ligand-Linker Conjugates 12 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 cIAP1 Ligand-Linker Conjugates 12 the recognition of cIAP1 Ligand-Linker Conjugates 12 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 (20C25) or optical (16C19, 26)] to the ligand-receptor recognition event. The coupling of a recognition event to photoinduced electron transfer or a change in the electronic structure of the conjugated polymer produces changes in the luminescence, UV-visible absorption, or redox potential of the polymer (4, 5). Extensive research has been carried out by using conjugated polymers (derivatives of polydiacetylene, electrochemically polymerized polypyrrole, or polythiophene) as chromic (16C19) or electrochemical (20C25, 28C31) biosensors. However, the relatively low sensitivity of UV-visible absorption measurements, the complex electrochemical instrumentation required, and the nonspecific interactions between biomolecules and conjugated polymers have prevented practical and general use. Water-soluble conjugated polymers (conjugated polyelectrolytes) show potential for use as a new class of high-sensitivity rapid-response chemical and biological sensors (26, 33, 34). The fluorescence of cIAP1 Ligand-Linker Conjugates 12 these polymers can be quenched by very small amounts of charged molecules (quenchers) that quench the excited state by energy transfer or electron transfer Slc4a1 (26, 35, 36). This quenching can be adapted to biosensing by coupling a quencher to a biological ligand. In aqueous solution, the photoluminescence (PL) from the polymer is quenched when the quencherCligand conjugate associates with the polyelectrolyte to form a relatively weak conjugateCpolymer complex, as a consequence of electrostatic and hydrophobic interactions. Exposure of the conjugateCpolymer complex to a biological receptor results in formation of a biospecific receptorCconjugate complex and release of the polymer with concomitant unquenching of the polymer fluorescence. In this paper, we report an investigation of the PL from a conjugated polyelectrolyte complex in aqueous solution. We show that the anionic conjugated polymer alone is subject to nonspecific effects on the PL (luminescence enhancement), which complicates the use of conjugated polyelectrolytes in biosensing applications. We find, however, that when a cationic polymer is added in the solution to associate with the anionic conjugated polyelectrolyte and form a charge neutral complex (CNC) [formed in aqueous solution by an anionic conjugated polyelectrolyte and a saturated cationic polyelectrolyte at a 1:1 ratio (per repeat cIAP1 Ligand-Linker Conjugates 12 unit)], the CNC shows little evidence of nonspecific interactions with biopolymers that occur.