**3.2. Nanoporous materials for enzyme entrapping**

Obviously, the capacitive range is in agreement with the sizes of the p-NOI structure form

**Figure 6.** The CV analysis for a AC sweep for VG between −10 V and +10 V for two adjacent metal fingers like source and gate of a p-NOI structure with 5 nm film thickness and similar size as in **Figure 1**, for low frequency (100 Hz) and high

The proposed pesticide biosensor works with acetylcholinesterase noted by AChE, with the code—EC 3.1.1.7. This receptor element is used to degrade agonists of the acetylcholine (AcH) neurohormone. In the living matter, AcH is present at neuromuscular junction and in the cholinergic nervous system, modulating the electrical pulse transmission at synaptic spaces, as other neurotransmitters [25]. The AChE has a very high catalytic affinity for acetylcholine and for its agonists as parasympathomimetic pesticides. This property opens the door of

The pesticides are intensively used in agriculture usually as organochlorines, carbamates, and organophosphate. Paraoxon belongs to the organophosphate class, being an oxon and the active metabolite of the parathion pesticide. Their working principle on the pests is based on the inhibition of AChE, allowing acetylcholine to transfer nerve impulses indefinitely and causing paralysis. Paraoxon is a novel generation of pesticide, which reacts as an inhibitor of AChE. Pesticides from this group act directly by stimulating the nicotinic receptors or indirectly by the inhibition of cholinesterase, as an acetylcholinesterase inhibitor, abbreviated as AChEI. Paraoxon is one of the most potent acetylcholinesterase inhibitor available in insecticide [27]. In water solvent, it stands for a high risk

**3. The work principle of the pesticide biosensor with nanoporous Si**

(**Figure 1**) and varies between 6 × 10−17 and 1.2 × 10−16 F/μm (**Figure 6**).

pesticide-selective detection by AChE-based enzyme biosensors [26].

**layer**

**3.1. Work principle**

frequency (1 THz).

196 Green Electronics

This section depicts the paraoxon biosensor starting from a Si wafer technology. Some intermediate nanoporous materials are used in the biosensor construction, for the enzyme entrapping. Among these materials, TiO2 [29], Al2 O3 [13], or porous Si still exists [30]. The porous material integration on a silicon wafer is starting by the first metal deposition, followed by subsequent processing steps, in order to convert them into compounds and finally into a porous matrix. The main steps of porous Si layer formation are:


This porous Si technology provides usual porous Si layers with a porosity of 56, suitable for the enzyme entrapping process [30].

These intermediate porous materials augment the capillary, allowing the biomaterials entrapping in a liquid phase, during the pre-deposition technological stage. At the same time, the porous layer must be grown onto the Si wafer in order to be strongly anchored to substrate and in order to avoid accidental detachments. Nanoporous Si can be easily converted from a Si thin upper layer. Having a closer lattice constant with Si, the porous Si stands for an efficient intermediate material for the next technological steps. The nanoporous Si material preparation by anodization is a perfect compatible method with the microelectronics technology. The pore sizes can be simply adapted in respect with the anodization reaction parameters, changing the electrolyte composition. Due to an increased area, offered by the nanoporous Si material against the monocrystalline Si, an enhanced miniaturization with capacitive electrodes can be performed. Therefore, the porous Si was selected as intermediate layer for the AChE enzyme entrapping. This solution is also in agreement with the nowadays tendency.
