Optical detection of pesticides and drugs based on chemiluminescence–fluorescence assays

Abstract

The paper illustrates two different concepts for monitoring pesticides and drugs. In the first approach double stranded deoxyribonucleic acid (dsDNA) was used as the sensing material, which intercalated drugs with high affinity. The intercalation of drugs such as Chlorpromazine (CP), Clomipramine (CM) and Imipramine (IP) were investigated. The assay was based on competition between the drug molecule and a fluorescent dye (ToPro-3) for intercalation with dsDNA. The ToPro3 was excited at 642 nm and the emission at 661 nm was detected using a fiber fluorimeter. A linear range of 25–100, 50–200 and 25–100 μM was obtained for CP, CM and IP, respectively. The sensitivity for both CP and CM was 0.14 while it was 0.06 mV/μM for IP. The detection limit was 1.25 μM in all cases. In another approach the detection of the pesticide 2,4-dichlorophenoxyacetic acid (2,4-D) was investigated based on chemiluminescence detection. The assay was based on competition between the binding of horseradish peroxidase (HRP) labeled versus unlabeled 2,4-D, on immobilized anti-2,4-D monoclonal antibodies (mAbs). Two other peroxidases from tomato (MOP) and tobacco (TOP) were also employed as labels for the 2,4-D assays. The assays were optimized by testing various chemiluminescent substrates for improving the signal intensity and sensitivity of the assays. Based on colorimetry a linear range of 0.35–20 and 0.7–4 μg/ml was obtained for TOP and MOP conjugates, respectively. However, using chemiluminometry both TOP and MOP showed a linear range of 0.5–5000 ng/ml. TOP demonstrated a higher specific activity compared to MOP and HRP. A detection limit of 50 pg/ml for 2,4-D was obtained using TOP conjugate and chemiluminescence detection. Both the fluorimetric and chemiluminometric assays were carried out in glass microcapillaries and detected using a computer coupled photomultiplier tube (PMT) as a photon detector. The responses were also compared with microtitre plate based colorimetric assay.