The transport properties of single-strand DNA probe-modified self-propelling micromachines are exploited for "on-the-fly" hybridization and selective single-step isolation of target nucleic acids from "raw" microliter biological samples (serum, urine, crude E. coli lysate, saliva). The rapid movement of the guided modified microrockets induces fluid convection, which enhances the hybridization efficiency, thus enabling the rapid and selective isolation of nucleic acid targets from untreated samples. The integration of these autonomous microrockets into a lab-on-chip device that provides both nucleic acid isolation and downstream analysis could thus be attractive for diverse applications.

A motion-based chemical sensing involving fuel-driven nanomotors is demonstrated. The new protocol relies on the use of an optical microscope for tracking changes in the speed of nanowire motors in the presence of the target analyte. Selective and sensitive measurements of trace silver ions are illustrated based on the dramatic and specific acceleration of bimetal nanowire motors in the presence of silver. Such nanomotor-based measurements would lead to a wide range of novel and powerful chemical and biological sensing protocols.Considerable recent efforts have been devoted to the development of artificial nanomotors. 1 In particular, fuel-driven bisegment Au-Pt nanowires exhibit autonomous self-propulsion due to electrocatalytic decomposition of hydrogen peroxide fuel. 1,2 Such autonomous motion of catalytic nanowire motors holds great promise for exciting applications ranging from drugdelivery, nanoscale assembly and transport, or motion-based biosensing. 1 This Communication reports on the first example of using catalytic nanomotors for motionbased chemical sensing, and particularly for specific detection of trace silver ions. During recent experiments in our laboratory involving electrochemically-triggered motion of catalytic nanowire motors 3 we observed unusual speed acceleration associated with silver ions NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript generated at a pseudo silver-wire reference electrode placed in the vicinity of the nanowire motors. Such unexpected specific silver effect upon the speed of catalytic nanomotors has been exploited in the present work for designing a new motion-based silver sensing protocol. The new protocol relies on the use of an optical microscope for tracking the speed of nanowire motors and offers highly selective, sensitive and simple measurements of trace silver based on direct visualization. Figure 1A displays traces of Au-Pt nanomotors (over a 3 second period), taken from videos of the nanowires in the presence of eleven different cations (100 µM each), along with the peroxide fuel. Ten of these cations caused a significant speed reduction, including a Brownian motion or a slower non-Brownian motion (with speeds ranging from 0.3 to 7.1 µm s −1 ). Such slow speed (compared to a actual speed of ~10 µm s −1 observed without these salts) is consistent with the self-electrophoresis mechanism for the propulsion of catalytic nanomotors, 4 where the speed decreases linearly with the solution conductivity. 5 In contrast, the nanomotors move over a dramatically longer path in the presence of silver (shown in the middle), displaying an average speed of 52 µm s −1 . Also shown in Figure 1 (B) is the histogram depicting the average speed of the nanomotors in the presence of the different cations tested. These data, along with the corresponding video (shown in the SI; Video 1), clearly illustrate the remarkably selective acceleration in the presence of silver. Adding other cations (e.g., Pb 2+ or K + up to 5 µM) had only slight reductions...

Motion control is essential for various applications of man-made nanomachines. The ability to control and regulate the movement of catalytic nanowire motors is illustrated by applying short heat pulses that allow the motors to be accelerated or slowed down. The accelerated motion observed during the heat pulses is attributed primarily to the thermal activation of the redox reactions of the H(2)O(2) fuel at the Pt and Au segments and to the decreased viscosity of the aqueous medium at elevated temperatures. The thermally modulated motion during repetitive temperature on/off cycles is highly reversible and fast, with speeds of 14 and 45 microm s(-1) at 25 and 65 degrees C, respectively. A wide range of speeds can be generated by tailoring the temperature to yield a linear speed-temperature dependence. Through the use of nickel-containing nanomotors, the ability to combine the thermally regulated motion of catalytic nanomotors with magnetic guidance is also demonstrated. Such on-demand control of the movement of nanowire motors holds great promise for complex operations of future manmade nanomachines and for creating more sophisticated nanomotors.

Highly conductive boron-doped diamond (BDD) electrodes are well suited for performing electrochemical measurements of nucleic acids in aqueous solution under diffusion-only control. The advantageous properties of this electrodic material in this context include reproducibility and the small background currents observed at very positive potentials, along with its robustness under extreme conditions so offering promising capabilities in future applications involving thermal heating or ultrasonic treatment. tRNA, single and double stranded DNA and 2'-deoxyguanosine 5'-monophosphate (dGMP) have been studied and well defined peaks were observed in all cases, directly assignable to the electro-oxidation of deoxyguanosine monophosphate.

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A new electrically heated carbon paste electrode has been developed for performing adsorptive stripping measurements of trace nucleic acids. Such coupling of electrochemistry at electrically heated electrodes with adsorptive constant-current stripping chronopotentiometry offers distinct advantages for trace measurements of nucleic acids. The application of increased temperatures during the deposition step results in dramatic (4-34-fold, depending on temperature applied) enhancement of the stripping signal. Such improvement is attributed to the accumulation step at the heated electrode. Forced thermal convection near the electrode surface facilitates the use of quiescent solutions and hence of ultrasmall volumes. Using an electrode temperature of 32 degrees C and a quiescent solution during the 1-min accumulation, the response is linear over the 1-8 mg/L range tested, with a detection limit of 0.5 mg/L. Such electrode heating technology offers great promise for various applications involving thermal manipulations of nucleic acids.

An electrochemically-controlled movement of catalytic nanomotors, including a cyclic 'on/off' activation of the nanomotor motion and a fine speed control, is illustrated.

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