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An electrochemical aptamer-based sensor was developed for glutamate, the major excitatory neurotransmitter in the central nervous system. Determining glutamic acid release and glutamic acid levels is crucial for studying signal transmission and for diagnosing pathological conditions in the brain. Glutamic acid-selective oligonucleotides were isolated from an ssDNA library using the Capture-SELEX protocol in complex medium. The selection permitted the isolation of an aptamer 1d04 with a dissociation constant of 12 µM. The aptamer sequence was further used in the development of an electrochemical aptamer sensor. For this purpose, a truncated aptamer sequence named glu1 was labelled with a ferrocene redox tag at the 3′-end and immobilized on a gold electrode surface via Au-thiol bonds. Using 6-mercapto-1-hexanol as the backfill, the sensor performance was characterized by alternating current voltammetry. The glu1 aptasensor showed a limit of detection of 0.0013 pM, a wide detection range between 0.01 pM and 1 nM, and good selectivity for glutamate in tenfold diluted human serum. With this enzyme-free aptasensor, the highly selective and sensitive detection of glutamate was demonstrated, which possesses great potential for implementation in microelectrodes and for in vitro as well as in vivo monitoring of neurotransmitter release. [ABSTRACT FROM AUTHOR]

Herein, an electrochemical aptamer biosensor based on a gold multielectrode array is reported for the detection of adenosine triphosphate (ATP), which is an important neurotransmitter in the central nervous system. The aptasensor possesses 64 individually addressable microelectrodes with a diameter of 24 μm, which is distributed over an area of 1 mm2. The electrodes are modified with an ATP‐specific aptamer, which is labeled with a ferrocene redox probe. It is demonstrated that the used chip fabrication and cleaning process generate microelectrode channels with similar electrochemical responses and electroactive surface areas. The immobilization of the aptamer on gold microelectrodes is optimized and the receptor density is determined to be (1.0 ± 0.44) × 1013 molecules cm−2. Concentration‐dependent alternating current voltammetry measurements exhibit a limit of detection of 0.30 × 10−9 m and a sensitivity of 2.4 nA logC. Furthermore, the sensor shows a high selectivity over analogous molecules and reproducible detection results in artificial cerebrospinal fluid. The sensor array is used to detect ATP via several channels of the same chip, showing high signal redundancy. A label‐free electrochemical, multichannel ATP aptasensor is demonstrated with high selectivity and subnanomolar sensitivity, which may be conducive to record this neurotransmitter in neuronal cell‐culture systems. [ABSTRACT FROM AUTHOR]

A novel dual‐signal ratiometric electrochemical biosensor based on a split aptamer is developed. A common shortcoming of amperometric aptamer sensors is unspecific signaling due to ssDNA conformational flexibility. Herein, a ratiometric detection using two competitive redox‐labeled aptamer strands is proposed. The neurotransmitter dopamine (DA) is chosen as a model target due to its importance for signal processing in the central nervous system. A DA aptamer is split into two parts, S1 and S2, where strand S1 is tethered to the electrode, whereas the second strand is labeled with methylene blue (MB) and acts as a redox reporter. Another ssDNA strand (CS1) tagged with anthraquinone (AQ) is introduced, which is complementary to strand S1 and reports on surface‐tethered strands that remain in its virgin state. In the presence of DA, CS1 is released from the surface due to the formation of S1–S2–DA complexes, resulting in decreasing AQ and increasing MB Faraday currents. Furthermore, logic gate operations can be performed to either improve signal reliability or enlarge the detection range. This proof‐of‐concept study demonstrates that the splitting of a full aptamer into two parts together with the use of complementary ratiomeric tests can improve the reliability of the sensor response. [ABSTRACT FROM AUTHOR]

With CCRF-CEM as the model cell, a highly sensitive and selective cytosensor was developed by taking advantage of polydopamine nanospheres for the first time. The strategies of aptamer/membrane protein recognition and Exonuclease III assisted cycle amplification were used for improving selectivity and sensitivity. The detection of limit reached was as low as 15 cells per mL. [ABSTRACT FROM AUTHOR]

• PEG blocking enhances malaria biomarker PfLDH detection in human serum. • Morphological composition of aptamer/PEG monolayer depends on PEG incubation time. • Long PEG incubation times lead to phase separation of aptamer and PEG molecules. • PfLDH detection in full human serum with LOD of 1.49 pM. • Type of blocking molecule has no influence of sensor sensitivity. Better approaches are critically needed for in situ point-of-care diagnostic biosensors that enable primary care physicians, or even individual patients, to directly analyze biological fluids without complicated sample pretreatments. Additional purification steps consume time, consume reagents, often require other equipment, and can introduce false-negative results. Biosensors have been modified with blocking molecules to reduce biofouling; however, the effectiveness relies on their chemical composition and morphology. Here, we used a polyethylene glycol film to suppress unspecific binding from human serum on an electrochemical malaria aptasensor. A detailed study of the variation of the chemical and morphological composition of the aptamer/polyethylene glycol mixed monolayer as a function of incubation time was conducted. Higher resistance to matrix biofouling was found for polyethylene glycol than for hydrophobic alkanethiol films. The best sensor performance was observed for intermediate polyethylene glycol immobilization times. With prolonged incubation, phase separation of aptamer, and polyethylene glycol molecules locally increased the aptamer density and thereby diminished the analyte binding capability. Remarkably, polyethylene glycols do not affect the aptasensor sensitivity but enhance the complex matrix tolerance, the dynamic range, and the limit of detection. Careful tuning of the blocking molecule immobilization is crucial to achieving high aptasensor performance and biofouling resistance. [ABSTRACT FROM AUTHOR]