BCSI created the TrakPod® line in 2016, and since this time, several changes have been made to the sensor manufacturing process. Some of these changes have had a noticeable impact on the final sensor products by improving sensor-to-sensor variability, while other changes have improved manufacturing speed and efficiency.
What Is The sv2 Sensor?
The sv2 sensor is a modified optical cuvette that contains a sample of culture media for pH tracking. The sensor fits into a fiber optic fixture and includes a membrane at the bottom of the liquid well. The membrane is impregnated with a fluorescent dye that emits characteristic wavelength spectra at different pH levels. During measurement, the fiber optic uses flashes of green light to excite the dye in the membrane and induces fluorescent light emissions. The intensities of these emissions are collected by photo-detectors in the TrakPod, which then calculates a wavelength ratio and converts it to a pH value.
The sv2 sensor is the key to tracking pH fluctuation due to shifting chemistry in media. Changes in pH from incubator equipment, lab operations or differing culture conditions are reflected in the fluorescent emission ratios from the sv2 sensor and converted into pH values.
How Are They Made?
sv2 sensor manufacturing consists of 5 critical steps to produce high-quality sensors.
1. Create The Dye-Protein Conjugate
A dye-protein conjugate is created between BCSI’s proprietary fluorescent dye and recombinant protein- this creates a stable molecule that can now be immobilized thanks to the protein component of the conjugation process.
Improvements
BCSI has implemented processes to increase the efficacy and speed of conjugate manufacturing, including formulating more direct chemical reactions to produce better production efficiency and by reducing intermediate production steps.
2. Immobilize Fluorescent Conjugate Onto The Membrane
After prepping the conjugate, a large fluorescent membrane is created using nitrocellulose. Following assorted rinsing and drying steps, the membrane now has conjugate dye incorporated into it such that the entire membrane exhibits fluorescent characteristics.
Improvements
Several improvements have been implemented during this immobilization step that reduce sensor-to-sensor variability, including:
- Optimizing uniform immobilization across the membrane
- Alterations to washing protocols
- Improved drying processes to reduce sv2 sensor membrane variability
3. Incorporate Fluorescent Membrane Disks Into sv2 Cups
The large fluorescent membrane is then used to manufacture hundreds of sensors. Each ¼” diameter circle is punched out of the membrane to best fit into the polystyrene strip well. These strip wells are transparent with flat bottoms to allow light to travel through the cup and pass between the membrane fragment and the TrakPod sensor fixture. A heat stake device is used to attach the membrane into the well.
Improvements
Improvements to the mechanical cutting device have reduced the potential for debris build-up and have improved the overall speed in which sensors are prepared. By studying the effects of different temperatures and times on membrane fixation, BCSI has also determined the optimal settings to produce uniform sensors each time and reduce sensor-to-sensor variability.
4. Packaging and EO Sterilizing The sv2 Sensors
The heat-staked and separated wells are then packaged into individual sterilization bags and are Ethylene Oxide (EO) treated. The EO process uses gas concentration, temperature, humidity, and exposure time to best decontaminate products using EO gas. The sv2 sensors are then returned to BCSI and calibration is performed.
Improvements:
BCSI monitors EO cycle parameters to maintain uniform sensor performance and calibrates sv2 sensors using TrakPod gold standard instruments to achieve pH value accuracy.
5. pHID Assignment
Using representative sampling, a series of sensors are characterized by exposing them to phosphate buffer(s) and IVF media. The resulting values are then used to assign a specific pHID, which is then confirmed through QC testing. An accurate and unique pHID is critical to determine the pH of test media. Once a pHID is determined, the sealed sterilized sensors are kitted and distributed to customers globally.
Improvements
BCSI has improved its sensor calibration process by using temperature controlled Trakpods to match normal media incubation temperatures.
sv2 Sensor Performance
Each lot of sensors have an expected variance tolerance of ±0.05 pH units. sv2 sensor pH values correspond well with pH values collected using a blood gas analyzer (BGA) and have a similar reading capacity (but every thirty minutes) without the need to perform lengthy calibration steps.
sv2 sensors have also been tested for accuracy in the presence of multiple potential interfering substances, including:
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Phenol Red
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Variable Protein Supplementation
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Variable Salt Concentration
Our interfering substance findings, complemented by the site standardization procedure guarantee that regardless of the media type you are using, pH can accurately be monitored.
In Comparison to Alternate pH Devices
Most technologies available for pH measurement are limited. Current protocols require a medium sample to be measured as point-in-time value, usually using an inexpensive electrode-based pH meter or with an expensive and more accurate blood gas analyzers (BGA). These methods provide a snapshot of the pH level at the time of collection and are subject to human error during sampling. Both BGA and electrode-based pH meters also require additional calibration steps before use.
The TrakStation pH monitoring technology is unique in its utilization of pH-sensitive fluorescent dye. The non-invasive and disposable sv2 sensor is designed so that it does not take up valuable culture dish space in the incubator while collecting pH data non-invasively every 30 minutes for up to 7 days.
Susan Olds
Embryology Product Specialist
Blood Cell Storage, Inc.
Tel: +1.425.654.8462 (D)
Email: susan.olds@safesens.com