Development of Amine group modified silicon nanowire and integrated with microfluidic for lead ion detection

This study describes the development of a chemical sensor that is portable, reliable, and rapid in the detection of lead ions. The developed sensor is based on silicon nanowire which distinguishes lead ions from ions present in water after the surface of the device was modified with 3-aminopropyl triethoxysilane (APTES) amino acid group which interacts with ions based on the mechanism of electronegativity of the element. This research broadly covers various important aspects of silicon nanowires and microfluidic devices for the creation of reliable chemical sensors. Also, this study created a new method of detecting lead ions by amine group modified silicon nanowire integrated with polydimethylsiloxane (PDMS) microfluidic. A new chemical sensor concept and implementation specifically developed to accurately detect lead ions in water through sensor modified with (3-aminopropyl) triethoxysilane (APTES) connected to microfluidic channel which send the sample to the sensing domain thereby decreasing the sensor response time by driving fluid through capillary phenomenon without undergoing diffusion or advection phenomenon. A silicon (Si) nanostructure was prepared using photolithography techniques, the device was fabricated via dry oxide etching approach with a controlled oxygen flow rate in oxidation furnace, network of uniform Si nanowires were successfully fabricated. Further, the device was functionalized with (3-aminopropyl) triethoxysilane (APTES) to serve as a sensor for heavy metal detection. The amino-functionalized Si nanowires were tested against the heavy metal lead ion (Pb+). The results indicated that Pb can be detected with high precision and selectivity, this was confirmed by atomic absorption spectroscopy in determining the level of lead content in water sample. The testing was carried with four (4) water samples, these include Tab water (H₂O), River H₂O, Treated (H₂O), DI (deionized) H₂O and found the levels of 0.0859 mg/L, 0.0929 mg/L, 0.0052mg/L, 0.0023 mg/L with 5.8pA, 7.2pA, 4.6pA, 3.3pA current responses, respectively. Thus, with this high response capabilities to the water samples, the sensor is effective for heavy metal detections and can be extended to a large sensor network in water treatment and monitoring plants. Further, new microfluidic bonding process based on SU8 cold pressed was implemented to achieve safe and reliable bonding. The requirement for a room temperature (cold pressed) process is particularly critical because the sensor must be functionalized with receptor molecules prior to bonding and cannot withstand significant heating after functionalization. Thus, the study developed new room temperature bonding method using SU8 as an intermediate adhesive layer. The SU8 modified bonding was compared with non-modified bonding. The bond strength of SU8 modified was found to be stronger than ordinary plasma bonding under the same curing conditions. Overnight room temperature curing and cold pressed yields an average burst pressure of 420 kPa, which is more than adequate for many PDMS sensor devices. In contrast, non SU8 coated plasma bonded resulted in a burst pressure of only 174 KPa.