The inner walls of gold nanotubules, prepared by template synthesis in the nanopores of polycarbonate track etch membranes, have been chemically modified with peptide nucleic acid (PNA) and used for label-free quantification of complementary DNA sequences. Selective binding of DNA to the PNA modified nanotubules are shown to decrease the flux of optically detected anionic markers through the nanotubules in a concentration-dependent manner. The strong dependence of the biorecognition-modulated ion transport through the nanopores on the ionic strength suggests a dominantly electrostatic exclusion mechanism of the ion flux decrease as a result of DNA binding to the PNA-modified nanopores.The extremely low detection limits required for bioanalysis are usually achieved with some chemical or physical amplification mechanism. 1,2 In ion channel-mimetic sensors, the target species functions as a stimulus, actuating (opening or closing) ion channels and, thus, modulating the flux of the marker ions to be detected. 3 Amplification is achieved because the concentration of markers exceeds the concentration of the target species by many orders of magnitude. In one approach, electrodes are modified with artificial receptors having intramolecular channels that can be blocked by the formation of inclusion complexes with the analyte and, thus, control the heterogeneous redox reactions of electroactive species. 4 Another method in these lines makes use of genetically and/or chemically engineered receptors built into cell membranes. 5-7 In a third approach based on gold nanopores, pioneered by the group of Martin, 8-10 limitations due to the fragility of lipid bilayer membranes, in which biological nanopores are suspended, are eliminated. Modulations of the ionic permeability due to polarity changes (hydrophobic to hydrophilic) 11 or steric effects (high molecular weight analytes binding to small molecular weight receptors in the nanopores) have already been explored. 12,13 In a previous study, we have demonstrated the feasibility of the ion channel-mimetic biosensing with gold nanoporous membranes modified by biotin. The selective recognition of avidin modulates the Ca 2+ ion transport, which is detected with ion-selective potentiometry. 13 Later, the protein detection system has been extended by using single conically shaped gold nanopores. 12In this paper, for the first time, gold nanopores are functionalized, with a peptide nucleic acid (PNA) 14 in view of a label-free detection of complementary DNA strands. The PNAs are shown to bind their complementary nucleic acid sequence 15 with higher affinity and specificity NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript compared with DNA probes. 16 The nanopores were prepared by electroless Au plating of track etch polycarbonate membranes. 10 In order to obtain regular pore diameters and better control of the plating process, the original recipe was slightly modified in that the membranes were dried in N 2 atmosphere before placing them in the Au pla...

A new hyphenated method utilizing FT-IR-attenuated total reflection (ATR) and electrochemical impedance spectroscopy (EIS) is presented to correlate the water uptake with concomitant potential and impedance changes of polymeric coated-wire electrodes (CWEs) and solid-contact ion-selective electrodes (SCISEs). The Ca(2+)-selective silicone rubber (RTV 3140) based SCISEs with poly(3-octylthiophene) (POT) as the solid-contact (SC) showed good correlation between a very low water content at the Pt-coated ZnSe substrate/SC interface and a superior potential stability. This is due to the hydrophobicity of both RTV 3140 and POT and the approximately 2 orders of magnitude lower water diffusion coefficients in POT compared to RTV 3140. Practically no potential drift could be observed during 24 h when unconditioned CaSCISEs were contacted with 10(-3) M CaCl(2), in contrast to the Ca(2+)-selective CWEs with considerably higher water uptake and potential drift. The CaSCISEs had a fast Nernstian response with a detection limit of 8 × 10(-9) M Ca(2+) and a good reproducibility and stability of the standard potential, which indicates that the CaSCISEs does not require any conditioning prior to use.

Pretty choosy: The selectivity filters of biological ion channels serve as inspiration for the development of ionophore‐modified solid‐state nanopores exhibiting extraordinary ion selectivity (see picture). Potentiometric transduction is introduced as a simple means to demonstrate the ion‐sensing capability of such nanopores.

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Effective recognition of enzymatically active tetrameric acetylcholinesterase (AChE) was accomplished by a hybrid nanofilm composed of a propidium-terminated self-assembled monolayer (Prop-SAM) which binds AChE via its peripheral anionic site (PAS) and an ultra-thin electrosynthesized molecularly imprinted polymer (MIP) cover layer of a novel carboxylate-modified derivative of 3,4-propylenedioxythiophene. The rebinding of the AChE to the MIP/Prop-SAM nanofilm covered electrode was detected by measuring in situ the enzymatic activity. The oxidative current of the released thiocholine was dependent on the AChE concentration from ca. 0.04 µM to 0.4 µM. An imprinting factor of 9.9 was obtained for the hybrid MIP, which is among the best values reported for protein imprinting.The dissociation constant characterizing the strength of the MIP-AChE binding was 4.2 ×10 −7 M indicating the dominant role of the PAS-Prop-SAM interaction, while the benefit of the MIP nanofilm covering the Prop-SAM layer was the effective suppression of the cross-reactivity towards competing proteins as compared with the Prop-SAM. The threefold selectivity gain provided by (i) the "shapespecific" MIP filter, (ii) the propidium-SAM, (iii) signal generation only by the AChE bound to the nanofilm show promise for assessing AChE activity levels in CSF.

We report the synthesis and analytical application of the first Cu2+‐selective synthetic ion channel based on peptide‐modified gold nanopores. A Cu2+‐binding peptide motif (Gly‐Gly‐His) along with two additional functional thiol derivatives inferring cation‐permselectivity and hydrophobicity was self‐assembled on the surface of gold nanoporous membranes comprising of about 5 nm diameter pores. These membranes were used to construct ion‐selective electrodes (ISEs) with extraordinary Cu2+ selectivities, approaching six orders of magnitude over certain ions. Since all constituents are immobilized to a supporting nanoporous membrane, their leaching, that is a ubiquitous problem of conventional ionophore‐based ISEs was effectively suppressed.

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We report on the synthesis and trace analytical application of ionophore-gold nanoparticle conjugates as a basis of a new concept in confining ionophores to ion-selective membranes using inert nanoparticle carriers.