Redox-Active Monolayers Self-Assembled on Gold Electrodes—Effect of Their Structures on Electrochemical Parameters and DNA Sensing Ability

Abstract

The background: The monolayers self-assembled on the gold electrode incorporated transition metal complexes can act both as receptor (“host” molecules) immobilization sites, as well as transducer for interface recognitions of “guest” molecules present in the aqueous solutions. Their electrochemical parameters influencing the sensing properties strongly depend on the transition metal complex structures. The objectives: The electrochemical characterization of the symmetric terpyridine–M2+–terpyridine and asymmetric dipyrromethene–M2+–terpyridine complexes modified with ssDNA probe covalently attached to the gold electrodes and exploring their ssDNA sensing ability were the main aims of the research presented. The methods: Two transition metal cations have been selected: Cu2+ and Co2+ for creation of redox-active monolayers. The electron transfer coefficients indicating the reversibility and electron transfer rate constant measuring kinetic of redox reactions have been determined for all SAMs studied using: Cyclic Voltammetry, Osteryoung Square-Wave Voltammetry, and Differential Pulse Voltammetry. All redox-active platforms have been applied for immobilization of ssDNA probe. Next, their sensing properties towards complementary DNA target have been explored electrochemically. The results: All SAMs studied were stable displaying quasi-reversible redox activity. The linear relationships between cathodic and anodic current vs. san rate were obtained for both symmetric and asymmetric SAMs incorporating Co2+ and Cu2+, indicating that oxidized and reduced redox sites are adsorbed on the electrode surface. The ssDNA sensing ability were observed in the fM concentration range. The low responses towards non-complementary ssDNA sequences provided evidences for sensors good selectivity. The conclusions: All redox-active SAMs modified with a ssDNA probe were suitable for sensing of ssDNA target, with very good sensitivity in fM range and very good selectivity. The detection limits obtained for SAMs incorporating Cu2+, both symmetric and asymmetric, were better in comparison to SAMs incorporating Co2+. Thus, selection of the right transition metal cation has stronger influence on ssDNA sensing ability, than complex structures.

Voltammetric Sensing of Chloride Based on a Redox-Active Complex: A Terpyridine-Co(II)-Dipyrromethene Functionalized Anion Receptor Deposited on a Gold Electrode

“…The gold electrode modified with the MBL, AHT/TPY/Co(II)/DPM-AR layer was characterized by the peak current and position of 0.78 µA and 410 mV, respectively, registered in 0.1 M NaNO 3 + 0.01 M H 3 BO 3 at pH 4.0 (Figure 2A, dashed black line). Initially, the concentration range of the system response towards Cl − was optimized to acquire optimal analytical parameters for the presented system [23,24]. The procedure of optimizing the concentration range was started from conducting experiments of detection of the chloride anions by the system proposed in the pM concentration range.…”

“…Based on the previously obtained results, we can conclude that Co(II) redox centers showed better selectivity towards Cl − than Cu(II) centers. In the present work, we have tested terpyridines as a possible coordination ligand [24]. The complexes of Co(II) with TPY and a dipyrromethene functionalized anion receptor (DPM-AR) were deposited on a gold electrode for sensing Cl − using SWV.…”

Trends in biosensing platforms for SARS-CoV-2 detection: A critical appraisal against standard detection tools

“… Sensitivity towards the samples matrix effect and poor stability are the bottleneck of biosensing technology. [ 115 , 116 ] …”

Recent advances and challenges in electrochemical biosensors for emerging and re-emerging infectious diseases

“…Numerous electrochemical biosensors have been proposed for identification of various diseases, citing features such as low cost, sensitivity, selectivity and rapid response, in recent years [ [11] , [12] , [13] , [14] , [15] , [16] ]. Electrochemical biosensors, a subsidary of biological sensors, comprise of a biological sensing system and an electrochemical transducer.…”

“… Method Advantages Disadvantages References Cell culture systems Isolate wide variety of viruses (including mixed cultures & unanticipated agents); Highly sensitive over rapid antigen tests; Antiviral susceptibility testing, epidemiologic studies and serotyping possible Technical expertise required to read cytopathic effect; Long incubation period for most viruses; Needs an in-house procurement and maintenance of a variety of cell culture forms [ 6 , 17 ] IF assays Usually exhibits good sensitivity and excellent specificity Not as sensitive as cell cultures; Not useful for all viruses; Requires trained experienced hands in reading results; poor adenovirus sensitivity [ 17 , 18 ] Molecular approach (Nucleic acid detection) Excellent specificity and sensitivity; Quick turnaround using PCR in real time; Suitable for viruses which cannot be cultivated in conventional cell cultures FDA-cleared kits and approved protocols not commonly available for most viruses; In-house technical skills needed to establish and standardize the methods; expensive instrumentation; Highly specific probes and primers (may skip mutated virus); Detects only the sought viruses and may miss mixed infections and unexpected agents in most cases; Most assays available only at research labs [ [19] , [20] , [21] ] Electrochemical biosensors Rapid response, cost-effective, robust, easy to miniaturize, excellent detection limits, requires less sample volume, has the ability to be used in turbid biological fluids with optically absorbing and fluorescent molecules. Conversion to a sensor device significantly reduces cost of analysis, saves time & enable regions with limited resources to perform healthcare diagnostics without the need of trained professionals Sensitive to sample matrix effects; Not as sensitive as conventional methods; Lower shelf life [ [11] , [12] , [13] , [14] , [15] , [16] ] …”