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

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 affini ty. The intercalation of drugs such as Chlorpromazine (CP), Clomipramine (C M) and Imipramine (IP) were investigated. The assay was based on competitio n between the drug molecule and a fluorescent dye (ToPro-3) for intercalati on 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 an d 25-100 muM was obtained for CP, CM and IP respectively. The sensitivity f or both CP and CM was 0.14 while it was 0.06 mV/muM for IP. The detection l imit was 1.25 muM in all cases. In another approach the detection of the pe sticide 2,4-dichlorophenoxyacetic acid (2,4-D) was investigated based on ch emiluminescence detection. The assay was based on competition between the b inding of horseradish peroxidase (HRP) labeled versus unlabeled 2,4-D, on i mmobilized anti-2,4-D monoclonal antibodies (mAbs). Two other peroxidases f rom tomato (MOP) and tobacco (TOP) were also employed as labels for the 2,4 -D assays. The assays were optimized by testing various chemiluminescent su bstrates for improving the signal intensity and sensitivity of the assays. Based on colorimetry a linear range of 0.35-20 and 0.7-4 mug/ml was obtaine d far 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 det ection. Both the fluorimetric and chemiluminometric assays were carried-out in glass microcapillaries and detected using a computer coupled photomulti plier tube (PMT) as a photon detector. The responses were also compared wit h microtitre plate based calorimetric assay. (C) 2001 Elsevier Science B.V. All rights reserved.