Published on 08 October 2024
Microfluidic biochips are revolutionary in biomedical research and diagnostics, allowing precise fluid manipulation [1]. However, their vulnerability to material-level attacks, particularly targeting polydimethylsiloxane (PDMS) microvalves, poses significant security risks [2]. Figure 1 illustrates the threat model.
This study introduces “BioTrojans,” chemically tampered microvalves designed to evade detection, and demonstrates how these material-level attacks can compromise flow-based microfluidic biochips (FMBs). The research also proposes countermeasures to mitigate such attacks.
Fig. 1: Material-level threat model for FMBs: The process begins with a customer placing an order for an FMB, which is received by the FMB company (route 1). Customers may include research institutions, forensic laboratories, pharmaceutical and biotechnology companies, clinical diagnostic laboratories, hospitals, healthcare providers, and retailers. The order is then relayed to the design unit (route 2), which subsequently sends the design files to the manufacturing unit, either in-house or third-party (route 3). At this stage, an attacker present in the manufacturing unit, who has full access to materials and the fabrication process, can carry out a material-level attack via chemical tampering, compromising the FMB. The compromised FMB proceeds to the quality control unit (route 4), where it evades detection due to the short duration testing and is ultimately delivered to the customer (route 5). Moreover, the attack vectors concerning the chemical tampering could be several, such as altering the curing ratio, modifying curing conditions, doping with harmful chemicals and reactive solvents, substituting the original PDMS precursor or curing agent liquid with an expired or contaminated one, and causing chemical degradation by deliberate exposure to heat, light, or radiation prior to fabrication.
How can you detect and prevent material-level attacks on PDMS microvalves before they compromise your microfluidic system?
The researchers modified the PDMS curing ratio (curing precursor to curing agent ratio, standard would be 10:1) to simulate BioTrojan attacks, which resulted in the mechanical failure of compromised microvalves when subjected to low-frequency cyclic actuations. To study this behavior in detail, finite element analysis (FEA) was employed to model the mechanical response of the microvalves under varying conditions. To ensure precise control over the actuation process, the team developed a Python script integrated with the Elveflow pressure control system. This setup allowed for automated control of pressure inputs and real-time monitoring of actuation cycles, enabling the team to accurately measure the point of failure for each microvalve.
Materials:
BioTrojans, PDMS valves fabricated with altered PDMS curing ratios (30:1 and 50:1), ruptured quickly under 2 Hz cyclic actuation, while authentic 10:1 ratio-valves remained intact.
The finite element model indicated that BioTrojans store significantly more mechanical energy, making them prone to rupture.
Movie 1 shows the low-frequency BioTrojan attack. This video showcases a ruptured BioTrojan valve with a 30:1 curing ratio, which withstood only around 45 seconds of alternating low-frequency cyclic actuations before failure. In contrast, the 10:1 valve remained intact, showing no signs of fracture even after two full days of similar testing.
To mitigate the threat posed by BioTrojan attacks in microvalve systems, a comprehensive security-by-design approach is crucial.
One effective countermeasure involves incorporating fillets into the PDMS layers, which are plasma bonded to the microvalve membrane. Fillets, often used in engineering to reduce stress concentrations, have proven beneficial in enhancing the durability of microvalves. By incorporating filleted edges, stress concentrations are minimized, reducing the chances of rupture during actuation. The introduction of fillet results demonstrate a significant decrease in peripheral stress and strain, particularly in the out-of-plane direction, reducing deformation and crack initiation at the edges of the microvalve membrane that emphasizes their effectiveness in preventing structural failure.
In addition to the design improvements, we propose a non-destructive spectral authentication technique utilizing mechanoresponsive fluorescent dye-doped microvalves [2]. This innovative technique leverages the sensitivity of these dye-doped microvalves to mechanical strain, allowing real-time authentication during actuation. By establishing a strain-spectral response calibration curve, compromised BioTrojan valves can be identified during quality control trials. The spectral shift response can easily differentiate authentic valves from BioTrojan-modified valves, providing an efficient method for detecting potential attacks without disrupting the system.
These combined approaches—stress-reducing fillets and spectral authentication—create a robust defense against BioTrojan attacks, safeguarding the integrity of microvalves. Quality control teams in biochip companies can utilize these detection techniques to safeguard biochips at different points along the supply chain, ensuring that compromised components are identified before they reach critical stages of deployment. Implementing these countermeasures can significantly enhance the reliability of microvalves in critical biomedical devices and ensure the protection of sensitive diagnostic operations.
The introduction of BioTrojan attacks underscores a critical security vulnerability in flow-based microfluidic biochips. This research demonstrates the need for robust security-by-design measures, including mechanical design improvements and advanced detection methods like fluorescence-based authentication. Future work will focus on enhancing countermeasure strategies and developing more resilient biochips.
Dr. Navajit Singh Baban is currently a postdoctoral associate at NYU’s Center for Cyber Security, focusing on securing microfluidic biochips. Additionally, he works on biomechanics, particularly bioinspired fracture and adhesion mechanics for nature-inspired innovation. He holds a B.Tech. degree in Mechanical Engineering from VIT University, Vellore, and an M.Tech. in Materials Science from the Indian Institute of Technology, Kanpur. He obtained his Ph.D. as a Global Ph.D. Fellow from the Department of Mechanical and Aerospace Engineering at NYU, USA, in 2021. As a firm supporter of nature-based innovation, he deeply values the inscrutable wisdom of natural solutions and aims to discover and incorporate them into his research.
Author’s web link: https://navajitsinghbaban.com/
This research was expertly guided by Prof. Ramesh Karri of New York University and Prof. Krishnendu Chakrabarty of Arizona State University. Their leadership in microfluidics and biochip security was key to advancing this study on viscoelastic microvalve-based attacks and innovative countermeasures.
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