Biosensors & Bioelectronics 17 (2002) 283 – 288 Gold-coated capillary based 2,4-dichlorophenoxyacetic acid chemi-luminescent assays: possibilities towards multianalysis Kumaran Ramanathan*, Anatoli Dzgoev, Juraj Svitel, Birgitta Rees Jo ¨ nsson, Bengt Danielsson Department of Pure and Applied Biochemistry, Box 124, Center for Chemistry and Chemical Engineering, Lund Uniersity, S -221 00 Lund, Sweden Received 26 July 2000; accepted 14 June 2001 Abstract The application of gold-coated glass capillaries for the design of a sensitive chemiluminescent immunoassay for 2,4-dichlorophe- noxyacetic acid (2,4-D) is reported. The gold coating on the glass capillaries has been partially characterized and its effect on enhancing the signal intensity has been measured. A simple photo-multiplier tube-based photon detector is used for this purpose. At least three times improvement in the signal intensity is observed compared to uncoated glass capillaries, with a consequent improvement in the sensitivity of detection. Using such gold-coated glass capillaries, 2,4-D in the range 10 -9 to 10 -13 mol/l is detectable at a precision of 15% (CV%) and a limit of detection of 10 -15 mol/l is achievable. The possibility of using such gold-coated capillaries with a portable multianalytical set-up for field studies is also demonstrated. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Capillaries; Assays; Acid www.elsevier.com/locate/bios 1. Introduction In general, pesticides are chemicals that may be synthetic or natural in origin, used for the control of insects, fungi, bacteria, weeds, nematodes, rodents and other pests. (Rogers and Mascini, 1998; Mulchandani et al., 1999). In order to minimize their ill effects on humans and animals, it is important to invent sensitive and fast techniques for detection and estimation of pesticide levels (Rogers et al., 1999) in water, fruits, vegetables, etc. Several kinds of assays have been developed for the monitoring of pesticides, especially for the monitoring of 2,4-dichlorophenoxy acetic acid (2,4-D). These in- clude, microtitre plate based enzyme linked immuno- sorbent assay (Revoltella et al., 1998), chromatography based assay (Onnerfjord and Marko-Varga, 2000), opti- cal fiber based assay (Mosiello et al., 1997), fluorimetric assay (Rogers et al., 1997), electrochemical assay (Kro ¨ ger et al., 1998), thermometric assay (unpublished data), molecular imprinting based assay (Surugiu et al., 2000) and assays based on other detection principles (Horacek and Skladal, 1997; Eremin et al., 1998). In earlier studies, we had reported the use of pat- terned thick film based microformat immunoassay for 2,4-D using a charge coupled device (CCD) based detector (Dzgoev et al., 1997). In another approach, a novel tobacco peroxidase (Gazaryan et al., 1998) was employed for application in an immunoassay for 2,4-D (Dzgoev et al., 1999). Very recently, we have also reported (Juraj et al., 2000) the application of con- canavalin A and 2,4-D conjugates for a renewable surface SPR assay for 2,4-D. A gold-coated glass capil- lary based chemiluminescence assay for 2,4-D is demonstrated in this report. The use of glass microcapillaries (Jiang et al., 1995) for such an immunoassay was advantageous due to their higher (internal) surface to volume ratio and efficient guiding of photons to a suitable detector, compared to microtitre plate based assays. Also micro- * Corresponding author. Present address: USEPA, 944 E. Harmon Av., Las Vegas, NV 89119, USA. E-mail address: alamelu6703@hotmail.com (K. Ramanathan). 0956-5663/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S0956-5663(01)00296-2