Analytical Sciences

Ultrasensitive Biosensor for Detection of Organophosphorus Pesticides Based on a Macrocycle Complex/Carbon Nanotubes Composite and 1-Methyl-3-octylimidazolium Tetrafluoroborate as Binder Compound

Neuma das Mercês PEREIRA,*1 Fernando Mota de OLIVEIRA,*1 Nara Rúbia PEREIRA,*2 Rodrigo Moreira VERLY,*1 Dênio Emanuel Pires SOUTO,*3 Lauro Tatsuo KUBOTA,*3 Auro Atsushi TANAKA,*4 Flavio Santos DAMOS,*4 and Rita de Cássia Silva LUZ*4

*1 Departamento de Química, UFVJM, 39100-000, Diamantina, MG, Brazil
*2 Instituto de Ciências Exatas e Biológicas, UFOP, 35400-000, Ouro Preto, MG, Brazil
*3 Instituto de Química, UNICAMP, P. O. Box 6154, 13083-970, Campinas, SP, Brazil
*4 Departamento de Química, UFMA, 65080-805, São Luís, MA, Brasil

This work describes the highly sensitive detection of organophosphorus pesticides employing the cobalt(II) 4,4,4,4-tetrasulfo-phthalocyanine (CoTSPc) macrocycle complex, carbon nanotubes (CNT), and 1-methyl-3-octylimidazolium tetrafluoroborate (OMIM[BF₄]). The technique is based on enzyme acetylcholinesterase (AChE) inhibition. The composite was characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, and amperometry. The AChE was immobilized on the composite electrode surface by cross-linking with glutaraldehyde and chitosan. The synergistic action of the CoTSPc/CNT/OMIM[BF₄] composite showed excellent electrocatalytic activity, with a low applied potential for the amperometric detection of thiocholine (TCh) at 0.0 V vs. Ag/AgCl. The calculated catalytic rate constant, k_cat, was 3.67 × 10³ mol⁻¹ L s⁻¹. Under the optimum conditions, the inhibition rates of these pesticides were proportional to their concentrations in the ranges of 1.0 pmol L⁻¹ to 1.0 nmol L⁻¹ (fenitrothion), 2.0 pmol L⁻¹ to 8.0 nmol L⁻¹ (dichlorvos), and 16 pmol L⁻¹ to 5.0 nmol L⁻¹ (malathion).

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