Biosensors from conjugated polyelectrolyte complexes

Abstract

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.

Figure 1

(A) Chemical structures. (B) Schematic of the DNP-BS⁻ sensor. (Ba) PL from CNC is quenched by DNP-BS⁻ and recovered on the specific binding between DNP-BS⁻ and anti-DNP antibody. (Bb) PL from CNC is quenched by DNP-BS⁻ and not recovered on addition of nonspecific antibody–rat IgG. (Bc) PL from CNC is quenched by TNP and not recovered on addition of nonspecific anti-DNP antibody.

Figure 2

(A) PL changes caused by interaction with biopolymers. Antibody enhances PL of MBL-PPV. PL from 9.5e⁻⁷ M MBL-PPV in 1×PBS (dashed line) and PL when 150 nM mouse IgG was added (solid line). (B) PL from 9.5 × 10⁻⁷ M MBL-PPV in 1×PBS is quenched by anti-mouse Fab′-Q (8 × 10⁻⁸ M) and “recovered” by the addition of specific antibody, mouse IgG (1.5 × 10⁻⁷ M) and nonspecific antibody, anti-DNP (1.3 × 10⁻⁷ M), respectively. PL from 9.5e⁻⁷ M MBL-PPV in 1×PBS is enhanced by the addition of mouse IgG (1.5 × 10⁻⁷ M). (C) Formation of CNC minimizes the nonspecific changes in PL by biopolymers. PL from 9.3e⁻⁶ M CNC in 1×PBS (solid line) and PL after adding 240 nM rat IgG (dashed line). (D) The quenched PL from CNC (by methyl viologen and DNP-BS⁻) is not affected by addition of rat IgG. PL from 9.3 × 10⁻⁶ M CNC was quenched by 35% when 2.3 × 10⁻⁶ M of MV²⁺ was added. There is less than 5% change in PL by the addition of 2.8 × 10⁻⁷ M rat IgG. The PL from 9.3 × 10⁻⁶ M CNC is not affected by the addition of 2.3 × 10⁻⁷ rat IgG alone.

Figure 3

(A) CNC quenching/unquenching by DNP-BS⁻/anti-DNP IgG. PL from the complex (MBL-PPV 3 × 10⁻⁶ M) was quenched on addition of successively greater concentrations of DNP-BS⁻. The quenched PL was recovered when antibody was added, with the ratio of DNP-BS⁻/anti-DNP IgG roughly 2:1. (B) Biological specificity of antigen control experiment: quenched PL from the CNC (by TNP) was not recovered on addition of anti-DNP IgG. PL from CNC (9.3 × 10⁻⁶ M) was quenched by about 9% by TNP (7.8 × 10⁻⁷ M), and no PL recovery on addition of 4.1 × 10⁻⁷ M anti-DNP IgG was observed. (C) Biological specificity of antibody control experiment: PL from 9.3 × 10⁻⁶ M CNC was quenched 11% when 1.2 × 10⁻⁵ M DNP-BS⁻ was added. No PL enhancement was found by the addition of 1.1 × 10⁻⁶ M rat IgG.