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Wireless communication has become commonplace in the consumer market. However, the potential of this technology to improve measurement capabilities, workflow, safety, and convenience in the laboratory is just beginning to be realized. The most immediate need in this market, and area of first adoption, has been for the monitoring of environmental conditions. This includes temperature and humidity tracking in the lab itself as well as for critical pieces of equipment such as freezers, refrigerators, and incubators. The networking capabilities of Wi-Fi and direct communication abilities of Bluetooth technology have allowed for the development of systems for real-time remote surveillance as well as intervention in case a critical parameter is breached. RFID communication is another technology that has begun to be used for needs such as convenient, automatic tracking of samples for chain-of-custody assurance in clinical laboratories.
While these technologies have started to be used for laboratory monitoring and tracking, there has been a lack of basic equipment that uses wireless communication to optimally measure and control parameters of a reaction or formulation itself in real time. This article reports on an effort to introduce these types of wireless technologies into one of the most ubiquitous tools in the laboratory—the magnetic hotplate stirrer—and how they can be used to make thermal reaction control more convenient than ever before.
The ability to monitor and control the temperature of a reaction or process is a basic, critical requirement in the laboratory setting. The electric hotplate has a long history and has evolved from a simple analog heat source to a programmable instrument with temperature sensing and control. Despite the fact that these types of platforms have been in the laboratory market for decades, there are still real problems centered around temperature control, monitoring, and recording that require advances in the state-of-the-art for optimal solutions.
An age-old challenge in setting up chemical reaction apparatus is how to accommodate a thermal probe to measure the temperature directly within the solution. This becomes especially difficult when trying to measure the solution temperature within a sealed or controlled-atmosphere reaction container or hard-to-reach places within multicomponent setups. Adding to the inconvenience is the wiring associated with the digital temperature sensors necessary for automatic thermal control. Specialized glassware has had to be developed in order to accommodate thermal probes in these types of systems and introduce expense and inherent failures point in any setup.
Interestingly, the related problem of mixing a solution in difficult-to-access or sealed containers has already been solved using wireless technology—in the form of the magnetic stir bar. This technology involves having a rotating magnet in a base unit and an associated free-spinning magnetic rod in the solution to be stirred. The two magnets are magnetically coupled and allow for stirring of the solution, controlled from outside of the container. This technology has been integrated into hotplates for a long time and is now standard equipment in every lab.
It was recognized at the start of this project that integrating temperature-sensing capabilities into a magnetic stir bar, as well as the ability to wirelessly communicate the data back to the hotplate itself, allows for direct measurement and thermal control of the solution without the need for wired probes and their associated issues. This provides the unique ability to measure and control the temperature in a completely sealed container without specialized glassware and probe adaptors and increases the convenience of any measurement.
Passive high-frequency (HF) RFID wireless technology was chosen as the means of communication between the stir bar and the hotplate. Passive RFID technology involves a tag and a reader. Both the tag and the reader have a radio antenna in the form of a coil. The reader obtains information from the tag by sending out a radio signal at 13.56 MHz. A microprocessor in the tag can then harvest that energy and send back a modulated signal containing the desired information that the reader can detect and translate. A big advantage of this type of passive system is that the tag does not need a battery; instead it uses wireless inductive coupling with the reader for both power and communication. RFID can operate in the low-frequency (LF), high-frequency, or ultrahigh-frequency range (UHF). The researchers chose to use HF at 13.56 MHz in order to balance performance between data transfer speed, medium compatibility, and read distance.
The electronics for an RFID tag and a temperature sensor, including a microprocessor, an antenna, and a thermistor, were incorporated into the stir bar (see Figure 1). All components were assembled onto a printed circuit board (PCB) and encased, along with a neodymium magnet, in a solvent-resistant fluoropolymer plastic that was molded into the desired shape. The microprocessor used has the ability to interrogate the on-board thermistor and store calibration information as well as an electronic serial number. This allows for each stir bar to be uniquely identifiable and have its own calibration information with up to five calibration points. The temperature measurement, calibration values, and barcode information can be transmitted wirelessly from the stir bar to the base hotplate/stirrer through interrogation from an ISO15693-compliant RFID reader that is incorporated into the instrument.
Figure 1 – smartSENSE wireless, temperature-sensing stir bar (Gate Scientific, Milpitas, CA). All electronics necessary for temperature sensing, storage of electronic barcode and calibration information, and wireless communication are encased in a solvent-resistant fluoropolymer.
The hotplate/stirrer base instrument was designed to be the hub of the system and employs a 1-GHz Cortex-A8 Arm processor running a Linux operating system (see Figure 2). The programmable instrument controls the mixing speed of the stir bar, wirelessly interrogates the stir bar for temperature and calibration information, employs a feedback loop to control the solution temperature, logs all relevant data, and communicates wirelessly with a local network for remote monitoring, control, and logged data downloads.
Figure 2 – The Precision Hotplate (Gate Scientific) utilizes RFID reader technology to communicate wirelessly with the smartSENSE Stirbar to measure and control the temperature of the stirring solution. Wi-Fi technology is also integrated to allow for networking and real-time remote monitoring, control, and data-logging. Credit: Peter Medilek.
Wi-Fi capabilities with 802.11b/g/n standards and data transfer rates up to 150 Mbps were designed into the instrument to allow the hotplate to be connected to a local area network. Each instrument is then given its own IP address and has its own website for monitoring and control. A user can simply connect to the instrument’s IP address and monitor, control, and download logged data in the form of a convenient CSV file. This allows for networking of multiple instruments and users, as shown in Figure 3.
Figure 3 – Wireless networking capabilities of the Precision Hotplate allow for remote monitoring, thermal control, and data-logging.
In order to maximize options for communication, sensing, and data transfer, the instrument was also designed with ports for Ethernet, an external thermocouple, and USB connection. The system has the ability to be used in several modes. It can function like a classic hotplate stirrer where a temperature is set by the user and controlled by the wireless stir bar, an external probe, or the built-in plate sensor. Another mode runs scripts that execute temperature and/or stirring commands in sequence; still another mode allows for remote monitoring and control. Figure 4 demonstrates the ability of the system to wirelessly control the temperature of a solution within a completely sealed container and log and transfer the resulting data to a remote laptop.
Figure 4 – Actual data log downloaded from a multistep thermal protocol. The temperature of a stirred solution in a completely closed flask was controlled wirelessly using the smartSENSE Stirbar and Precision Hotplate.
This project has succeeded in introducing the latest wireless technologies into one of the core pieces of equipment used in the wet laboratory. The ability to measure and control temperature in applications such as fermentation, distillation, inert atmosphere reactions, titrations, pharmacy compounding, and any thermally controlled reaction is easier and more convenient on both the measurement side as well as the monitoring and data access side when using this platform. The data-logging and remote surveillance capabilities are ideal for use in GMP and regulated laboratory environments where traceability is paramount.
One of the key take-aways from this work is that wireless technology can be used in the laboratory in ways that go beyond simple environmental tracking. The ability to measure and control reactions and experiments with in situ wireless sensors enables ease of setups that have not been previously possible and allow for the tightest experimental or process control possible. Gate Scientific is actively working to incorporate wireless sensing and networking capabilities into other tools to fully realize the potential of the technology to enhance measurement and control capabilities in the modern laboratory.
KrisScaboois CTO, Gate Scientific Inc., 950 Yosemite Dr., Milpitas, CA 95035, U.S.A.; tel.: 650-223-5509; e-mail: [email protected]; www.gatescientific.com