Digital microfluidic biochips (DMFBs) integrated with processors and arrays of sensors form cyberphysical systems and consequently face a variety of unique, recently described security threats. It has been noted that techniques used for error recovery can provide some assurance of integrity when a cyberphysical DMFB is under attack. This paper proposes the use of such hardware for security purposes through the randomization of checkpoints in both space and time, and provides design guidelines for designers of such systems. We define security metrics and present techniques for improving performance through static checkpoint maps, and describe performance tradeoffs associated with static and random checkpoints. We also provide detailed classification of attack models and demonstrate the feasibility of our techniques with case studies on assays implemented in typical DMFB hardware.

Secure Randomized Checkpointing for Digital Microfluidic Biochips

Present security study involving analysis of manipulation of individual droplets of samples and reagents by digital microfluidic biochip has remarked that the biochip design flow is vulnerable to piracy attacks, hardware Trojans attacks, overproduction, Denial-of-Service attacks, and counterfeiting. Attackers can introduce bioprotocol manipulation attacks against biochips used for medical diagnosis, biochemical analysis, and frequent diseases detection in healthcare industry. Among these attacks, hardware Trojans have created a major threatening issue in its security concern with multiple ways to crack the sensitive data or alter original functionality by doing malicious operations in biochips. In this paper, we present a systematic algorithm for the assignment of checkpoints required for error-recovery of available bioprotocols in case of hardware Trojans attacks in performing operations by biochip. Moreover, it can guide the placement and timing of checkpoints so that the result of an attack is reduced, and hence enhance the security concerns of digital microfluidic biochips. Comparative study with traditional checkpoint schemes demonstrate the superiority of the proposed algorithm without overhead of the bioprotocol completion time with higher error detection accuracy.

Checkpoints Assignment on Cyber-Physical Digital Microfluidic Biochips for Early Detection of Hardware Trojans

Cyberphysical microfluidic biochips comprise a broad set of technologies for the manipulation of fluids. This chapter provides a general review of microfluidic technologies with an emphasis on digital and flow-based microfluidic biochips, as they have shown great promise for commercialization and integration with security technologies. We discuss basic principles, fabrication, and advances in design automation.

Cyberphysical Microfluidic Biochips

As an emerging lab-on-a-chip technology platform, digital microfluidic biochips (DMFBs) have been widely used for executing various laboratory procedures in biochemistry and biomedicine such as gene sequencing and near-patient diagnosis, with the advantages of low reagent consumption, high precision, and miniaturization and integration. With the ongoing rapid deployment of DMFBs, however, these devices are now facing serious and complicated security challenges that not only damage their functional integrity but also affect their system reliability. In this article, we present a systematic review of DMFB security, focusing on both the state-of-the-art attack and defense techniques. First, the overall security situation, the working principle, and the corresponding fabrication technology of DMFBs are introduced. Afterwards, existing attack approaches are divided into several categories and discussed in detail, including denial of service, intellectual property piracy, bioassay tampering, layout modification, actuation sequence tampering, concentration altering, parameter modification, reading forgery, and information leakage. To prevent biochips from being damaged by these attack behaviors, a number of defense measures have been proposed in recent years. Accordingly, we further classify these techniques into three categories according to their respective defense purposes, including confidentiality protection, integrity protection, and availability protection. These measures, to varying degrees, can provide effective protection for DMFBs. Finally, key trends and directions for future research that are related to the security of DMFBs are discussed from several aspects, e.g., manufacturing materials, biochip structure, and usage environment, thus providing new ideas for future biochip protection.

A Survey on Security of Digital Microfluidic Biochips: Technology, Attack, and Defense

In the area of biomedical engineering, digital-microfluidic biochips (DMFBs) have received considerable attention because of their capability of providing an efficient and reliable platform for conducting point-of-care clinical diagnostics. System reliability, in turn, mandates error-recoverability while implementing biochemical assays on-chip for medical applications. Unfortunately, the technology of DMFBs is not yet fully equipped to handle error-recovery from various microfluidic operations involving droplet motion and reaction. Recently, a number of cyber-physical systems have been proposed to provide real-time checking and error-recovery in assays based on the feedback received from a few on-chip checkpoints. However, to synthesize robust feedback systems for different types of DMFBs, certain practical issues need to be considered such as co-optimization of checkpoint placement, error-recoverability, and layout of droplet-routing pathways. For application-specific DMFBs, we propose here an algorithm that minimizes the number of checkpoints and determines their locations to cover every path in a given droplet-routing solution. Next, for general-purpose DMFBs, where the checkpoints are pre-deployed in specific locations, we present a checkpoint-aware routing algorithm such that every droplet-routing path passes through at least one checkpoint to enable error-recovery and to ensure physical routability of all droplets. Furthermore, we also propose strategies for executing the algorithms in reliable mode to enhance error-recoverability. The proposed methods thus provide reliability-hardening mechanisms for a wide class of cyber-physical DMFBs.

Reliability Hardening Mechanisms in Cyber-Physical Digital-Microfluidic Biochips

In the area of biomedical engineering, digital-microfluidic biochips (DMFBs) have received considerable attention, because of their capability of providing an efficient and reliable platform for conducting point-of-care clinical diagnostics. System reliability, in turn, mandates error-recoverability while implementing biochemical assays on-chip for medical applications. Unfortunately, the technology of DMFBs is not yet fully equipped to handle error-recovery from various microfluidic operations involving droplet motion and reaction. Recently, a number of cyber-physical systems have been proposed to provide real-time checking and error-recovery in assays based on the feedback received from a few on-chip checkpoints. However, in order to synthesize robust feedback systems for different types of DMFBs, certain practical issues need to be considered such as co-optimization of checkpoint placement and layout of droplet-routing pathways. For application-specific DMFBs, we propose here an algorithm that minimizes the number of checkpoints and determines their locations to cover every path in a given droplet-routing solution. Next, for general-purpose DMFBs, where the checkpoints are pre-deployed in specific locations, we present a checkpoint-aware routing algorithm such that every droplet-routing path passes through at least one checkpoint to enable error-recovery and to ensure physical routability of all droplets. Our experiments on assay benchmarks show encouraging results in terms of latest-arrival-time and routability of droplets. The proposed methods thus provide convenient reliability-hardening mechanisms for a wide class of cyber-physical DMFBs.

Guan-Ming Huang

Papers

On reliability hardening in cyber-physical digital-microfluidic biochips