Expanding the informational chemistries of life: peptide/RNA networks.

The RNA world hypothesis simplifies the complex biopolymer networks underlining the informational and metabolic needs of living systems to a single biopolymer scaffold. This simplification requires abiotic reaction cascades for the construction of RNA, and this chemistry remains the subject of active research. Here, we explore a complementary approach involving the design of dynamic peptide networks capable of amplifying encoded chemical information and setting the stage for mutualistic associations with RNA. Peptide conformational networks are known to be capable of evolution in disease states and of co-opting metal ions, aromatic heterocycles and lipids to extend their emergent behaviours. The coexistence and association of dynamic peptide and RNA networks appear to have driven the emergence of higher-order informational systems in biology that are not available to either scaffold independently, and such mutualistic interdependence poses critical questions regarding the search for life across our Solar System and beyond.This article is part of the themed issue 'Reconceptualizing the origins of life'.

Design of multi-phase dynamic chemical networks.

Template-directed polymerization reactions enable the accurate storage and processing of nature's biopolymer information. This mutualistic relationship of nucleic acids and proteins, a network known as life's central dogma, is now marvellously complex, and the progressive steps necessary for creating the initial sequence and chain-length-specific polymer templates are lost to time. Here we design and construct dynamic polymerization networks that exploit metastable prion cross-ß phases. Mixed-phase environments have been used for constructing synthetic polymers, but these dynamic phases emerge naturally from the growing peptide oligomers and create environments suitable both to nucleate assembly and select for ordered templates. The resulting templates direct the amplification of a phase containing only chain-length-specific peptide-like oligomers. Such multi-phase biopolymer dynamics reveal pathways for the emergence, self-selection and amplification of chain-length- and possibly sequence-specific biopolymers.

Reversible electronic nanoswitch based on DNA G-quadruplex conformation: a platform for single-step, reagentless potassium detection.

A novel on/off electronic nanoswitch is for the first time described based on the conformational change of DNA sequence possessing a single guanine (G)-rich stretch. Here, a thiolated, amine-containing G-rich DNA sequence is immobilized on the surface of gold electrode by means of facile sulfur-gold chemistry, followed by being labeled with redox-active ferrocene molecules serving as the signaling species. The surface-confined DNA sequence is able to change its configuration between rigid tetramolecular G-quadruplex and flexible single-stranded structures. The large conformational change enables the probes to perform an inchworm like extending-shrinking motion, which is reflected by the fluctuation in current intensity that depends on the electron-transfer distance between the electrode surface and the redox labels. Since potassium ion can specifically bind to G-quadruplex, using this reagentless reusable electrochemical sensing platform, the simple, rapid and selective detection of potassium ion can be accomplished without the use of exogenous reagents. Success in the present electronic nanoswitch is expected to promote the exploitation of functional DNA-based nanosystems.

Reusable electrochemical sensing platform for highly sensitive detection of small molecules based on structure-switching signaling aptamers.

Aptamers are nucleic acids that have high affinity and selectivity for their target molecules. A target may induce the structure switching from a DNA/DNA duplex to a DNA/target complex. In the present study, a reusable electrochemical sensing platform based on structure-switching signaling aptamers for highly sensitive detection of small molecules is developed using adenosine as a model analyte. A gold electrode is first modified with polytyramine and gold nanoparticles. Then, thiolated capture probe is assembled onto the modified electrode surface via sulfur-gold affinity. Ferrocene (Fc)-labeled aptamer probe, which is designed to hybridize with capture DNA sequence and specifically recognize adenosine, is immobilized on the electrode surface by hybridization reaction. The introduction of adenosine triggers structure switching of the aptamer. As a result, Fc-labeled aptamer probe is forced to dissociate from the sensing interface, resulting in a decrease in redox current. The decrement of peak current is proportional to the amount of adenosine. The present sensing system could provide both a wide linear dynamic range and a low detection limit. In addition, high selectivity, good reproducibility, stability, and reusability are achieved. The recovery test demonstrates the feasibility of the designed sensing system for an adenosine assay.

Homogeneous, unmodified gold nanoparticle-based colorimetric assay of hydrogen peroxide.

An unmodified gold nanoparticle-based colorimetric assay system in homogeneous format has been developed using hydrogen peroxide (H(2)O(2)) as a model analyte. H(2)O(2) is added to o-phenylenediamine/horseradish peroxidase solution, and allowed to react for 10 min. Then, unmodified gold nanoparticles that serve as "reaction indicators" are added to the reaction solution. The resulting mixture color changes dramatically from red to blue. The reason is that azoaniline, a horseradish peroxidase-catalyzed oxidation product, induces the nanoparticle aggregation. Using this approach, H(2)O(2) can be semiquantitatively determined over the concentration range of approximately 4 orders of magnitude by the naked eye. If the observed peak intensity at 420 nm is used for the construction of the calibration plot, hydrogen peroxide can be accurately determined down to concentration levels of 1.3 x 10(-6) M. Compared with the conventional electrochemical protocol, this sensing system offers several important advantages: (1) ability to be monitored by the naked eye, (2) avoiding the need of surface modification of electrodes or gold nanoparticles and (3) detection in homogeneous solution. It is worthy of note that this efficient and convenient strategy is also suitable for the detection of other species, such as glucose and cholesterol.