Acetylcholinesterase (AChE) Electrodes Based on Gelatin and Chitosan Matrices for the Pesticide Detection

Figures & data

Figure 1. (a) Optimum pH of gelatin based AChE electrode (pH 7.0–8.2; potassium phosphate buffer (♦), pH 8.0–9.0; borate buffer (•). (b) Optimum pH of chitosan based AChE electrode. (pH 7.0–8.2; potassium phosphate buffer (♦), pH 8.0–9.5; borate buffer (•).

Figure 2. Optimum temperature of gelatin (•) and chitosan (▪) based AChE electrode (in 2.5 mM of phosphate buffer, pH 8.0 for gelatin based system and in 2.5 mM of borate buffer, pH 8.5 for chitosan based system).

Figure 3. Effect of AChCl concentration on gelatin (a) and chitosan (b) based AChE electrode (in 2.5 mM of phosphate buffer, pH 8.0 for gelatin based system and in 2.5 mM of borate buffer, pH 8.5 for chitosan based system, at 25°C).

Figure 4. Operational (♦; 25°C) and thermal (•; 37°C) stability of chitosan based AChE electrode.

Table 1. Effects of organic solvents on chitosan based AChE electrode (incubation time; 30 and 60 min)

	Activity (%)
	30 min	60 min
Toluen	106.7	106.7
Cyclohegzan	118	141
Dioxan	0	0
Aceton	0	0
Carbontetrachloride	89.3	64.3
İso-octan	93.5	83.9
Chloroform	29.4	17.7

Table 2. Effects of organic solvents on gelatin based AChE electrode (incubation time; 30 and 60 min)

	Activity (%)
	30 min	60 min
Toluen	110	110
Cyclohegzan	100	100
Dioxan	33.3	29.6
Aceton	63.6	63.6
Carbontetrachloride	95	95
İso-octan	100	100
Chloroform	68.2	68.2

Figure 5. Inhibition curves of malathion (a), parathion-methyl (b), and methamidophos (c) for gelatin based AChE electrode.

Figure 6. Inhibition curves of malathion (a), parathion-methyl (b), and methamidophos (c) for chitosan based AChE electrode.

Table 3. Reproducibility of gelatin and chitosan based AChE biosensors

	Concentration (C)	Standard deviation (SD)	Variation coefficient (cv)
Gelatin based AChE-biosensor
Malathion	0.6 × 10^−6 M	±0.13 × 10^−7 M	2.1%
Parathion-methyl	0.1 × 10^−6 M	±0.02 × 10^−7 M	1.3%
Methamidophos	0.1 × 10^−6 M	±0.005 × 10^−7 M	0.5%
Chitosan based AChE-biosensor
Malathion	0.6 × 10^−6 M	±0.13 × 10^−7 M	2.1%
Parathion-methyl	0.5 × 10^−6 M	±0.15 × 10^−7 M	3.8%
Methamidophos	0.5 × 10^−6 M	±0.14 × 10^−7 M	4.4%

Table 4. Regeneration of chitosan based AChE electrode inhibited by various organophosphates; malathion, parathion-methyl, and methamidophos (PAM-2; 0.1 mM in 2.5 mM sodium borate buffer (pH 8.5), 60 min)

Pesticide	Concentration (µM)	Inhibited electrode Activity (%)	Regenerated electrode Activity (%)
Malathion	0.1	94.3	100
	1	82.6	100
	10	74.5	98
	100	63.7	97.8
Parathion-methyl	0.1	88.5	100
	1	69.2	100
	10	4.3	93.8
	100	26.2	70
Methamidophos	0.1	85.7	100
	1	71.6	100
	10	47.8	100
	100	24.2	80

Table 5. Regeneration of gelatin based AChE electrode inhibited by various organophosphates (malathion, parathion-methyl, and methamidophos). PAM-2; 0.1 mM in 2.5 mM sodium borate buffer (pH 8.5), 60 min)

Pesticide	Concentration (µM)	Inhibited electrode Activity (%)	Regenerated electrode Activity (%)
Malathion	0.6	84	100
	6	70	100
	60	63.4	100
	600	53.8	84
Parathion-methyl	0.1	91.4	100
	1	78	100
	10	57.4	83.3
	100	31	66.6
Methamidophos	0.1	97.3	100
	1	78.6	100
	10	70	100
	100	50	80