Synthesis, characterization, and evaluation of ferrocene-theophylline conjugates for use in electrochemical enzyme immunoassay.
A series of 8-(ferrocenylalkyl)theophylline conjugates were synthesized for evaluation in a homogeneous, competitive electrochemical immunoassay for theophylline with amperometric detection of the ferrocene label at +320 mV. The electrical signal was amplified via redox cycling with the glucose oxidase/glucose system. The resulting catalytic current was strongly inhibited upon binding of the conjugates to anti-theophylline antibodies such that a large excess of theophylline was required to achieve complete reversal leading to an assay with poor sensitivity in the clinical range. A study of the nonspecific interaction of the antibodies with various ferrocene derivatives indicated that this was reduced when a charged functional group was present on the metallocene ring. Consequently, a conjugate was synthesized with a quaternary ammonium group which when incorporated into the assay resulted in improved sensitivity.
Forrow
Nigel J
NJ
MediSense (UK) Ltd., Abbott Laboratories, 14/15 Eyston Way, Abingdon, Oxon OX14 1TR, UK. nigel.forrow@abbott.com
Foulds
Nicola C
NC
Frew
Jane E
JE
Law
John T
JT
D000107:Acetylation; D000906:Antibodies / Q000737:chemistry / Q000276:immunology; D002138:Calibration; D002384:Catalysis; D004563:Electrochemistry; D005296:Ferrous Compounds / Q000737:chemistry*; D005949:Glucose Oxidase / Q000737:chemistry; D007124:Immunoenzyme Techniques; D007202:Indicators and Reagents; D009682:Magnetic Resonance Spectroscopy; D000075163:Metallocenes; D013806:Theophylline / Q000737:chemistry*
D000906:Antibodies; D005296:Ferrous Compounds; D007202:Indicators and Reagents; D000075163:Metallocenes; D013806:Theophylline; D005949:Glucose Oxidase; C004998:ferrocene