Reversible switches of DNA nanostructures between "Closed" and "Open" states and their biosensing applications

Interferon-γ detection in point of care diagnostics: Short review

Interferon (IFN)-γ is a cytokine secreted by immune cells. The elevated levels of IFN-γ are an early indicator of multiple diseases such as tuberculosis and autoimmune diseases. This short review focuses on different sensing methods based on optical, electrochemical, and mechanical principles. We explain how specific biorecognition molecules such as antibodies and aptamers are employed in the sensing methods. We also compare different surface functionalization methods and their details. Although the review gives an overview of only IFN-γ sensing, the same strategies can be applied to sensing other analytes with appropriate modifications.

Dual-ratiometric electrochemical aptasensor enabled by programmable dynamic range: Application for threshold-based detection of aflatoxin B1

Aptamer-based sensor with high-specificity typically has a fixed linear range due to the host-guest binding. To expand the dynamic range for multiple scenarios, we report here a dual-ratiometric electrochemical aptasensor that integrates two aptamer profiles with varied affinity into a single sensing interface for aflatoxin B1 (AFB1) detection. Using functional aptamer as recognition element and generator of signals, we fabricate the dual-ratiometric aptasensor with anthraquinone loaded reduced graphene oxide (AQ-rGO), methylene blue labeled hairpin DNA (MB-DNA), and ferrocene labeled linear aptamer (Fc-apt), using MB and Fc probes to work in tandem while AQ as reference. The current of Fc (I_Fc) is used to detect the low-concentration analyte, and that of MB (I_MB) varies when the concentration of AFB1 reaches a threshold. The threshold switch for I_MB could be tuned by engineering the quantity ratio of Fc-apt and MB-DNA (a ratio of 1:1 is used here). The aptasensor can rapidly achieve the positive (+)/negative (-) detection of AFB1 with a threshold concentration of 10 pg mL^-1, while the quantitative detection employs the ratio of current of AQ, MB, and Fc (i.e., I_AQ/I_MB and I_AQ/I_Fc) as yardsticks, offering two linear ranges of 10-10⁶ and 10^-2-5 × 10⁴ pg mL^-1, respectively. The aptasensor is successfully used to monitor the amount of AFB1 in a 7-days mildew process of peanut. Such a protocol opens a new way for the design of sensors with the programmable linear range in the advanced biological and chemical sensing.

Impedimetric Aptamer-Based Biosensors: Principles and Techniques

Aptamers are a specific class of ligands with high affinities comparable to antibodies, which are selected and synthesized in vitro. In combination with impedance spectroscopy as sensitive measurement method, we gain a class of biosensors with high potential for handheld devices and point-of-care tests. In this review, we report on recent advances in aptamer-based impedimetric biosensors. Besides giving a short summary of electrochemical measurement techniques, the most exciting innovative developments of detection strategies in the last decades are reviewed. Finally, important criteria for the comparison of aptamer-based biosensors are discussed.

DNA framework-engineered electrochemical biosensors

Self-assembled DNA nanostructures have shown remarkable potential in the engineering of biosensing interfaces, which can improve the performance of various biosensors. In particular, by exploiting the structural rigidity and programmability of the framework nucleic acids with high precision, molecular recognition on the electrochemical biosensing interface has been significantly enhanced, leading to the development of highly sensitive and specific biosensors for nucleic acids, small molecules, proteins, and cells. In this review, we summarize recent advances in DNA framework-engineered biosensing interfaces and the application of corresponding electrochemical biosensors.

Advanced biosensors for monitoring astronauts' health during long-duration space missions

Long-duration space missions pose important health concerns for astronauts, especially regarding the adverse effects of microgravity and exposure to high-energy cosmic rays. The long-term maintenance of crew health and performance mainly relies on prevention, early diagnoses, condition management, and medical interventions in situ. In-flight biosensor diagnostic devices and medical procedures must use few resources and operate in a microgravity environment, which complicates the collection and management of biological samples. Moreover, the biosensors must be certified for in-flight operation according to strict design and safety regulations. Herein, we report on the state of the art and recent advances in biosensing diagnostic instrumentation for monitoring astronauts' health during long-duration space missions, including portable and wearable biosensors. We discuss perspectives on new-format biosensors in autonomous space clinics. We also describe our own work in developing biosensing devices for non-invasively diagnosing space-related diseases, and how they are used in long-duration missions. Finally, we discuss the benefits of space exploration for Earth-based medicine.

The evolution of gadolinium based contrast agents: from single-modality to multi-modality

Gadolinium-based contrast agents are extensively used as magnetic resonance imaging (MRI) contrast agents due to their outstanding signal enhancement and ease of chemical modification. However, it is increasingly recognized that information obtained from single modal molecular imaging cannot satisfy the higher requirements on the efficiency and accuracy for clinical diagnosis and medical research, due to its limitation and default rooted in single molecular imaging technique itself. To compensate for the deficiencies of single function magnetic resonance imaging contrast agents, the combination of multi-modality imaging has turned to be the research hotpot in recent years. This review presents an overview on the recent developments of the functionalization of gadolinium-based contrast agents, and their application in biomedicine applications.

Graphene-Assisted Label-Free Homogeneous Electrochemical Biosensing Strategy based on Aptamer-Switched Bidirectional DNA Polymerization

In this contribution, taking the discrimination ability of graphene over single-stranded (ss) DNA/double-stranded (ds) DNA in combination with the electrochemical impedance transducer, we developed a novel label-free homogeneous electrochemical biosensor using graphene-modified glassy carbon electrode (GCE) as the sensing platform. To convert the specific aptamer-target recognition into ultrasensitive electrochemical signal output, a novel aptamer-switched bidirectional DNA polymerization (BDP) strategy, capable of both target recycling and exponential signal amplification, was compatibly developed in this study. In this strategy, all the designed DNA structures could be adsorbed on the graphene/GCE and, thus, serve as the electrochemical impedance signal reporter, while the target acts as a trigger of this BDP reaction, in which these designed DNA structures are bound together and, then, converted to long dsDNA duplex. The distinct difference in electrochemical impedance spectroscopy between the designed structures and generated long dsDNA duplex on the graphene/GCE allows label-free and homogeneous detection of target down to femto-gram level. The target can be displaced from aptamer through the polymerization to initiate the next recognition-polymerization cycle. Herein, the design and signaling principle of aptamer-switched BDP amplification system were elucidated, and the working conditions were optimized. This method not only provides a universal platform for electrochemical biosensing but also shows great potential in biological process researches and clinic diagnostics.

Ultrasensitive electrochemical detection of breast cancer cells based on DNA-rolling-circle-amplification-directed enzyme-catalyzed polymerization

An ultrasensitive cytosensor based on DNA-rolling-circle-amplification-directed enzyme-catalyzed polymerization is demonstrated. As a proof of concept, the cytosensor shows excellent sensitivity for MCF-7 cell detection with a lower detection limit of 12 cells per mL.

Simple and efficient method to purify DNA-protein conjugates and its sensing applications

DNA-protein conjugates are very useful in analytical chemistry for target recognition and signal amplification. While a number of methods for conjugating DNA with proteins are known, methods for purification of DNA-protein conjugates from reaction mixture containing unreacted proteins are much less investigated. In this work, a simple and efficient approach to purify DNA-invertase conjugates from reaction mixture via a biotin displacement strategy to release desthiobiotinylated DNA-invertase conjugates from streptavidin-coated magnetic beads was developed. The conjugates purified by this approach were utilized for quantitative detection of cocaine and DNA using a personal glucose meter through structure-switching DNA aptamer sensors and competitive DNA hybridization assays, respectively. In both cases, the purified DNA-invertase conjugates showed better performance compared to the same assays using unpurified conjugates. The approach demonstrated here can be further expanded to other DNA and proteins to generate purified DNA-protein conjugates for analytical and other applications.