Chemical-Induced pH-Mediated Molecular Switch

Abstract

The transmembrane protein α-hemolysin pore has been used to develop ultrasensitive biosensors, study biomolecular folding and unfolding, investigate covalent and non-covalent bonding interactions, and probe enzyme kinetics. Here, we report that by addition of ionic liquid tetrakis(hydroxymethyl)phosphonium chloride solution to the α-hemolysin pore, the α-hemolysin channel can be controlled open or closed by adjusting the pH of the solution. This approach can be employed to develop a novel molecular switch to regulate molecular transport, and should find potential applications as a ‘smart’ drug delivery method.

Layer by layer assembled films between hemoglobin and multiwall carbon nanotubes for pH-switchable biosensing

“…Electrochemical impedance spectroscopy (EIS) was performed in 0.10 M KCl solution including 1.0 mM Fe(CN) 6 3− /Fe(CN) 4− (1:1) as a supporting electrolyte at its open circuit potential with the AUTOLAB PGSTAT 302 N electrochemical working station (Metrohm Co. Ltd., Switzerland) accompanying with the frequency from 1.0 × 10 −3 to 1.0 × 10 5 Hz. All electrochemical measurements were performed with a CHI 660 C electrochemical working station (CH Instruments Co., USA) equipped with conventional threeelectrode system, in which the modified GCE (diameter 4 mm) was as the working electrode, a platinum wire and a saturated calomel electrode (SCE) were employed as the counter electrode and the reference electrode, respectively.…”

“…In this case, the electron transfer resistance, R et , is equal to the semicircle diameter in EIS. R et is the key parameter for the electron transfer kinetics of probe Fe(CN) 6 3− /Fe(CN) 6 4− at the electrode interface. On the other hand, the diffusion process could be characterized with the linear part at lower frequencies in EIS.…”

“…The study of molecular switches and memories has attracted much attention during the past decade owing to their potential function as the key component for manufacturing materials at molecular and electronics levels [1][2][3][4][5][6]. The development of the devices was mainly based on their controllable responses to external stimuli [7], such as stress [8], temperature [9], pH value [10], moisture [11], light [12], and ionic strength [13].…”

“…An advantage for those enzyme or protein based devices is that pH-controllable bioelectrocatalysis could be performed on the basis of direct electrochemistry of enzyme or protein. However, with the existence of electroactive mediators (such as Fe(CN) 6 3− ), direct electrochemistry of most enzymes or proteins could not be fully realized. As a result, their bioelectrocatalysis and the biosensing functions were significantly influenced due to the electroactive mediator.…”

“…Hb in the LBL film may provide a new interface for the study of electrochemical biosensors and other molecular biodevices (e.g., pH-dependent switch). Moreover, it is believed that such pH-sensitive "on-off" function benefited from porphyrin structure in the Hb molecules and the derived switchable actions at different pH values in the existence of mediator (Fe(CN) 6 3− ) [25]. As is well-known, multiwalled carbon nanotubes (MWCNTs) play important role in scientific and industrial fields and serve as an excellent matrix for promoting the electron transfer rate between solution and electrode owing to their great chemical stability, outstanding electrical conductivity and high mechanical strength [26,27].…”