**4.2. Electrode design and processing**

The biosensor transducer is represented by an electrical capacitance. From the design stage, the capacitor has a constant armature surface and a fix distance between electrodes, so that any variation in capacitance reflects the electrical permittivity change of the material. This permittivity variation is proportional with the quantity of ions accumulated after the enzymatic-assisted reaction of the pesticide hydrolysis. Therefore, in order to increase the sensor sensitivity, as high as possible, the active area is demanded high. In this sense, the electrodes are designed with an interdigitated geometry [31].

Now, **Figure 10** shows multiple metallic traces for a global view of the biosensor transducer.

**4.3. The enzyme processing step**

**Figure 9.** Mask of the metal overlap onto nanoporous Si material.

**Figure 8.** The porous Si mask.

link agent.

In the first step, the powder of the acetylcholinesterase enzyme is blended with serum albumin, all being of Sigma provenience. A phosphate buffer solution keeps pH = 7.1 as constant pH. The mixture has helped to be entrapped on the Si wafer surface by the adsorption method. In this scope, the glutaraldehyde, in solution of 2.5% concentration, is added as cross-

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**Figure 7.** The SEM image reveals the nanoporous material.

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**Figure 8.** The porous Si mask.

**4. Results of some key technological steps**

(**Figure 7**). When the anodization process is tested for 60 mA/cm2

The morphology of the synthesized porous Si film is characterized by SEM microscopy

crowded inside a single larger pore rather with a crater shape. When the anodization process

Then, **Figure 9** presents the next mask used for the metal deposition on nanoporous Si

The biosensor transducer is represented by an electrical capacitance. From the design stage, the capacitor has a constant armature surface and a fix distance between electrodes, so that any variation in capacitance reflects the electrical permittivity change of the material. This permittivity variation is proportional with the quantity of ions accumulated after the enzymatic-assisted reaction of the pesticide hydrolysis. Therefore, in order to increase the sensor sensitivity, as high as possible, the active area is demanded high. In this sense, the electrodes

Now, **Figure 10** shows multiple metallic traces for a global view of the biosensor transducer.

offered the optimum porosity for the enzyme entrapping [22].

**Figure 8** presents the designed mask for the nanoporous Si region configuration.

, some huge pores reached 7 μm size. However, the current density

, some multiple pores are

**4.1. Nanoporous Si characterization**

**4.2. Electrode design and processing**

are designed with an interdigitated geometry [31].

**Figure 7.** The SEM image reveals the nanoporous material.

is tested for 300 mA/cm2

of 50 mA/cm2

198 Green Electronics

material.

**Figure 9.** Mask of the metal overlap onto nanoporous Si material.

#### **4.3. The enzyme processing step**

In the first step, the powder of the acetylcholinesterase enzyme is blended with serum albumin, all being of Sigma provenience. A phosphate buffer solution keeps pH = 7.1 as constant pH. The mixture has helped to be entrapped on the Si wafer surface by the adsorption method. In this scope, the glutaraldehyde, in solution of 2.5% concentration, is added as crosslink agent.

proves that our capacitive biosensor works as a p-NOI capacitor, with enzyme on nanoporous Si material on Si substrate. The voltage ranging from negative values toward positive values brings the capacitor from the accumulation regime through the depletion regime the middle decreasing part of the curves—toward the inversion regime. The C-V curve is almost reproducible that indicates an adequate enzyme entrapping onto the silicon surface

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The chapter presented a biosensor generated by micro-nanotechnology and biotechnology to serve as a monitoring tool to ensure a green environment condition. The fabrication steps of an integrated pesticide biosensor with AChE enzyme on nanoporous Si structure were presented. The structure of interdigitated electrodes was investigated as physical phenomena simulations inside the novel proposed planar nothing on insulator (p-NOI) structure. The

• Fabrication of nanoporous Si layer onto the Si surface and characterization by CV

traces. The primary C-V curves checked the sensor functionality.

• The enzyme membrane immobilization technique by adsorption onto the porous Si layer

The growing technological process of the nanoporous Si layer onto the Si surface was processed by the conversion of the n-type wafer into a p-type at the surface, followed by anodization. The enzyme membrane immobilization technique was by adsorption onto the porous Si layer and fixed with glutaraldehyde by the cross-link method. Finally, the preparation of the capacitive electrodes as an interdigitated structure comprised 98 horizontal metallic p-NOI

This work was partially supported by a grant of the Romanian National Authority for Scientific Research and Innovation, CNCS/CCCDI UEFISCDI, project number PN-III-P2-2.1-

PED-2016-0427, within PNCDI III, project number 205PED/2017, for IMT part.

occurred.

**6. Conclusions**

**Acknowledgements**

contributions and purpose of this work were:

**Figure 12.** Detail of electrodes on the final product.

**Figure 10.** Final overlap of the metallic electrodes.

**Figure 11.** The top view of a piece of the enzymatic membrane.

The enzymatic area overlaps on the nanoporous Si area that facilitates the immobilization. The structure is introduced in drying stove for 24 hours. A top view of a piece of the processed AChE membrane is presented in **Figure 11**.
