# Sensor Micro and Nanoparticles for Microfluidic Application
## 5 Microfluidic Systems for Biomedical Applications
### Particle-Supported Electrochemical Detection Systems  
[PERSON] et al. [75] developed a portable electrochemical microfluidic system and presented a synthesis of nanocomposites onto a screen-printed electrode (SPE). Presented SPEs were functionalized by co-electrodeposition of self-assembled positively charged chitosan (CS), graphene oxide (GO), which was negatively charged, and nickel nanoparticle NiNPs with size of 31 nm. By using the prepared biosensor (CS-RGO-NiNPs), enzymeless detection of glucose (Glc) in human urine samples was performed in alkaline media. Cyclic voltammetry (CV) was applied for monitoring the electrocatalytic activity of CS-RGO-NiNP modified electrode towards glucose. Presence of 3 mM glucose caused an increase in anodic current and a decrease in cathodic current due to Glc oxidation. Nickel nanoparticle in CS-RGO-NiNPs nanocomposite acted as an enzyme mimicking catalyst for Glc oxidation into glucolactone by reduction into Ni (II) species. Due to this, Ni (II) concentration increased by creating an increase in anodic peak current. Highly sensitive and selective Glc sensing was possible in a wide linear range up to 9 mM with limit of detection of 4.1 mM.  
The most common from electrochemical measurements is amperometric detection in which the controlled electrical potential applied between a reference and a working electrode causes the oxidation or reduction in the electroactive analytes, and the induced electrical current at the electrode surface is recorded as the analytical signal. [PERSON]. [PERSON] et al. [29] presented a novel low-volume microfluidic immune assay system, which employed Au/chitosan/Fe3O4 composite, for specific recognition and analysis of hemoglobin A1c in blood samples. Due to Fe3O4 particle incorporation, the composite was easily controlled and transported by external magnetic field. The formed composite was also suitable for antihuman hemoglobin-A1c antibody (HbA1c mAb) immobilization with fine efficiency and good biocompatibility. After the injection of Au/chitosan/Fe3O4 into the microfluidic device, HbA1c mAb was immobilized by forming HbA1c mAb/Au/chitosan/Fe3O4 composite. Later, HbA1c was introduced into the microchannel and incubated for 8 min. Unbound HbA1c was washed out and then hemoglobin antibodies (Hb mAb) were injected and incubated. Finally, secondary alkaline phosphatase (AP)-conjugated antibody was injected, and immunoassay was ready to use. In the presence of 1-naphthyl phosphate(1-NP), an enzymatic reaction between a secondary AP-conjugated antibody and 1-NP occurred by producing the electroactive 1-naphth. It was demonstrated that the increase in anodic oxidation current of 1-naphth on the gold microelectrode was proportional to the HbA1c concentration. By optimizing electrophoresis and detection conditions, linear response of HbA1c in the concentration range from 0.05 to 1.5 \(\upmu\)g/mL was achieved with the detection limit of 0.025 \(\upmu\)g/mL. By comparing chitosan/Fe3O4 composite to Au/chitosan/Fe3O4, it was shown that antibody adhesion abilities were better when the sensor with assembled gold nanoparticles (Au/chitosan/Fe3O4) was applied. Moreover, by using the presented microfluidic immune assay, the cost per assay decreased due to the reduction in the consumed reagent amount. Another advantage of the presented assay was short assay time. Less than 30 min were needed to perform the whole detection process.