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Nano and Micro Technologies

Nano and Micro Technologies - Poster Session C

Poster J18 - Investigation of Fluid Flow Control for an Optical Cavity-based Biosensor using Low-cost vacuum pumps

Friday, October 25, 2024
10:00 AM – 11:00 AM EST
Location: Exhibit Hall E, F & G

Introduction:  Early and accurate diagnosis and monitoring of diseases is a key factor in improving survivability and outcomes for patients globally. The development of diagnostic biosensor technology is revolutionizing medical care around the world by providing highly selective, low-cost disease detections. While Enzyme-linked immunosorbent assay (ELISA) is the current gold standard for biomarker detection, it requires trained medical professionals, time, and economic resources. Point-of-care (POC) biosensors have recently been developed to enable affordable, accessible, and reliable early disease detection. POC testing is also known as bedside testing because the devices are operable at the location of the patient and do not require trained medical professionals for operation. This allows patients to receive a rapid diagnosis and monitor their conditions regardless of their locations or the economic and medical resources available. Our group has developed an optical cavity-based biosensor (OCB) for POC biomarker detection that is fabricated and tested with low-cost materials and components to detect a small concentration of a biomarker. One of the key features of using the OCB is a consistent and affordable method for controlling fluid flow during the measurements. In this presentation, we will present the results comparing commercially available low-cost vacuum pump options for our OCB and show how an additional resistive channel can be used to lower the flow rate further.

Materials and

Methods:  Optical cavity structures (OCS) were fabricated by depositing a silver layer on two glass substrates to create parallel mirror surfaces. Next, spin-on-glass from Futurrex (Southlake, TX) was deposited on top of both silver layers, and SU8 photoresist from Kayaku (Westborough, MA) was patterned on one side to form a cavity between the surfaces. Lastly, the substrates were bonded with UV glue from Norland Products (Jamesburg, NJ). Three OCSs with cavity widths of 11.9 micrometers were fabricated for testing four low-cost vacuum pumps from Amazon. Pump 1 is an Artshu brand pump ($9.89), pump 2 is a Jiawu ($9.09), pump 3 is from CrocSee ($14.99), and pump 4 is a Zopsc ($23.40). Each vacuum pump was tested at its minimum operational voltage and then at incremental voltages within the recommended range. Each OCS outlet was connected to Tygon tubing marked with 10 microliter intervals to quantify the flow rate. The tubing was connected to the vacuum pump powered by a DC power supply with variable voltage. 20 microliters of DI water were pipetted into the inlet of the OCS and the vacuum was turned on at the minimum operational voltage. The flow rate of water through the OCS was recorded using a timer. The flow rate was measured and recorded for all three OCSs at each voltage and compared for consistency. This was repeated for every vacuum pump within its respective voltage range. The noise level at every voltage for each vacuum pump was collected for 30 seconds and recorded.

Results, Conclusions, and Discussions: The average and standard deviation of the flow rate from three OCSs at each voltage for vacuum pumps 1, 2, 3, and 4, were calculated and displayed in Figure 1. For vacuum pump 1, the average flow rate ranged from 2.97 to 23.08 microliters per minute with a standard deviation range of .366 to 1.868. For vacuum pump 2, the average flow rate ranged from 8.46 to 44.13 microliters per minute with a standard deviation range of 2.686 to 8.453. For vacuum pump 3, the average flow rate ranged from 19.54 to 28.60 microliters per minute with a standard deviation range of 3.451 to 6.808. For vacuum pump 4, the average flow rate ranged from 4.10 to 42.14 microliters per minute with a standard deviation range from .330 to 4.467. The noise levels of all four vacuum pumps were similar (ranging between 48 to 81 decibels), so no pumps were excluded based on noise level. We determined the vacuum pump 1 is the best low-cost pump for our OCB due to its smallest standard deviation between the three OCSs, and therefore offered the most consistent flow. Often, a lower flow rate than 2.97 microliters per minute, the lowest possible flow rate with the vacuum pump 1, is desired for measurements. Therefore, a resistive channel was investigated to lower the flow rate to 1 microliter per minute range. A resistive channel was fabricated with the same fabrication process used for OCS except with a thinner SU8 layer to reduce the microfluidic channel height and flow rate range. The resistive channel was attached in series between the OCS and vacuum pump as shown in Figure 2. We achieved a 1.75 microliters per minute flow rate with a resistive channel with a channel height of 6 micrometers. Therefore, we successfully demonstrated that we can achieve consistent and reliable fluid flow in the range of 1.75 to 23.08 microliters per minute using the Artshu pump from Amazon together with a 6-micron resistive channel. We will also present the results of successful streptavidin detection with our OCB using this resistive channel and vacuum pump combination.

Acknowledgements (Optional):