PharmaSeq, Inc. has developed and exclusively offers a light-activated p-Chip (microtransponder) for a wide variety of applications to label, track, and authenticate items. This integrated system is used to identify laboratory mice and other small animals during research and clinical trials , and enables chain-of-custody tracking. This White Paper explains how the PharmaSeq p-Chip System works and discusses its reliability and cost effectiveness.
The p-Chip has also been used to study the social habits of ants [2, 6] and honey bees, in bioassays [3, 5] and to study cell growth .
THE P-CHIP SYSTEM FOR TAGGING
The key element of the PharmaSeq method is a tiny, silicon-based integrated circuit called a p-Chip. When activated by laser light, the p-Chip transmits a unique identification number via a reader to tracking software on a standard PC. The p-Chip is inert, durable, and easy to insert under the skin in the mouse’s tail. Once implanted, the p-Chip can be repeatedly and rapidly read at a workstation where other experimental parameters are being recorded (Figure 1). This provides safe and confident confirmation of the animal’s identity and experimental role throughout its lifetime.
The p-Chip is differentiated from other, traditional RFID (radio frequency identification) tags used for laboratory animals by being much smaller and far less expensive. This is why the PharmaSeq system offers a number of advantages over conventional tagging methods including no need for anesthetics during tagging and subsequent handling, less stress for the animal and greater system reliability. The system allows institutions to secure the value of a major experimental asset, laboratory animals, and to guarantee the integrity of experimental results.
The PharmaSeq system for small animal tagging consists of the following two key components:
- p-Chips preloaded in injectors, sterile, with optional injector handles
- a PharmaSeq Wand (ID reader)
The Wand is connected to a PC or a laptop running PharmaSeq’s p-Chip Reader software.
The p-Chip is an ultra-small electronic device (500 x 500 x 100 microns) that carries a unique identification number (ID) (Figure 2). An essential part of the p-Chip are photocells that, when illuminated by light from the Wand, provide power for the chip’s electronic circuits. Each p-Chip contains an on-chip antenna that transmits the chip’s ID through a variable magnetic field created close to the tag as a result of modulated current in the antenna loop. The current in the antenna is driven by onboard logic circuitry controlled by the contents of the p-Chip’s electronic memory (ROM). The memory capacity allows for over one billion different IDs. The ID range is sufficient, therefore, to distinguish between any two p-Chips produced in the majority of applications.
Stability and chemical inertness are key features that enable the use of p-Chips in laboratory animals and other biochemical applications. The reliability of the RF transmitting function was tested by exposing p-Chips to various aqueous solutions and solvents. The results show that the p-Chips are very stable in most neutral aqueous solutions, and moderately stable in acidic or basic solutions (half-life of about 1 day). They are also very stable in organic solvents: after a 15 day exposure, 80-100% of the chips maintained their RF performance in all of the organic solvents tested. The stability and inertness are due, in part, to the p-Chip’s silicon dioxide surface, which is deposited during the semiconductor manufacturing process as a final passivation layer. The surface of the device is glass-like, similar to other implantable microchips that come in glass capsules, an important property for biocompatibility. PharmaSeq, along with one of its partners, has performed long-term studies with implanted p-Chips in mice and observed no adverse histological effects .
p-Chips have excellent resilience to physical extremes: they can be heated up to 520 °C for 8 hours and still have full RF activity (sample size: 100 devices, all of which were fully active at the end of incubation). They have a lifetime of many years at room temperature or lower (-20 °C and -80 °C were tested). They withstand repeated freezing and thawing in liquid nitrogen. In addition, they are not affected by centrifugation (15 min at about 15,000 g), exposure to microwave radiation (1 hour exposure, standard 700 W microwave oven), or autoclaving (2,000 cycles). The stability of p-Chips in the presence of various environmental factors far exceeds the requirements for tagging laboratory animals. Further details on the PharmaSeq p-Chip system and its use can be found in references  through .
The p-Chip is injected subcutaneously in the tail of a mouse using a specially designed injector that consists of a disposable hypodermic needle and plunger assembly, all in a sterilized package (Figure 3). The injector is preloaded with a single p-Chip. The reusable handle provided snaps onto the injector for the implantation. No other assembly or preparation is required. p-Chips are read immediately after insertion, and the ID of the subject animal is registered into tracking software. Mice can generally be tagged approximately 14 days after birth, or later.
PHARMASEQ WAND (ID READER)
The PharmaSeq Wand (Figure 4) is a small, light-weight device capable of reading the IDs of individual p-Chips. It is connected to a conventional PC or laptop using an included USB cable that provides power and communication to the device. For mouse tagging it is usually mounted on a fixed stand to allow a technician to have both hands free for working with the animal. It can also be handheld. The ID is read when the implanted p-Chip is placed in the beam of light emitted by the Wand. Partially transparent material, such as a layer of skin, will not normally prevent reading.
The Wand consists of the following components: a laser diode with programmable laser driver, an optical focusing module, an air coil pickup connected to an RF receiver, an FPGA, a USB 2.0 microcontroller and power regulators. The laser emits 5 to 60 mW of optical power at 660 nm. Key characteristics of the Wand are listed in the Specifications section below.
The Wand − when placed over a p-Chip − energizes the p-Chip, determines the ID from the RF signals using internal onboard firmware, and reports the decoded ID via p-Chip Reader software. The ID readout from a valid RF signal is practically instantaneous (milliseconds), thus minimum handling time is required for an animal. To read an ID, the Wand must be placed within the p-Chip range, typically less than 7 mm, and a sufficient amount of light has to reach the p-Chip.
PERSONAL COMPUTER AND SOFTWARE
PharmaSeq’s p-Chip Reader software is a Windows-based program that is installed on the PC to which the Wand is attached. The software receives and processes the ID of each p-Chip as it is read from the animal. p-Chip Reader software is compatible with most Windows desktop applications such as Excel and Access, as well as enterprise software for animal colony and experimental management.