ABSTRACT
Bacteria can exploit mechanics to display remarkable plasticity in response to locally changing physical and chemical conditions. Compliant structures play a notable role in their taxis behavior, specifically for navigation inside complex and structured environments. Bioinspired mechanisms with rationally designed architectures capable of large, nonlinear deformation present opportunities for introducing autonomy into engineered small-scale devices. This work analyzes the effect of hydrodynamic forces and rheology of local surroundings on swimming at low Reynolds number, identifies the challenges and benefits of using elastohydrodynamic coupling in locomotion, and further develops a suite of machinery for building untethered microrobots with self-regulated mobility. We demonstrate that coupling the structural and magnetic properties of artificial microswimmers with the dynamic properties of the fluid leads to adaptive locomotion in the absence of on-board sensors.
ABSTRACT
The labelfree detection of nucleic acid sequences is one of the modern attempts to develop quick, cheap and miniaturised hand-held devices for the future genetic testing in biotechnology and medical diagnostics. We present an approach to detect the hybridisation of DNA sequences using electrolyte-oxide-semiconductor field-effect transistors (EOSFETs) with micrometer dimensions. These semiconductor devices are sensitive to electrical charge variations that occur at the surface/electrolyte interface, i.e. upon hybridisation of oligonucleotides with complementary single-stranded (ss) oligonucleotides, which are immobilised on the oxide surface of the transistor gate. This method allows direct, time-resolved and in situ detection of specific nucleic acid binding events without any labelling. We focus on the detection mechanism of our sensors by using oppositely charged polyelectrolytes (PAH and PSS) subsequently attached to the transistor structures. Our results indicate that the sensor output is charge sensitive and distance dependent from the gate surface, which pinpoints the need for very defined surface chemistry at the device surface. The hybridisation of natural 19 base-pair sequences has been successfully detected with the sensors. In combination with nano-transistors a PCR free detection system might be feasible in future.
Subject(s)
Biosensing Techniques/instrumentation , DNA Probes/chemistry , DNA/analysis , Electrochemistry/instrumentation , Oligonucleotide Array Sequence Analysis , Transducers , Transistors, Electronic , Biosensing Techniques/methods , DNA/chemistry , DNA/ultrastructure , DNA Probes/ultrastructure , Electrochemistry/methods , Equipment Design , Equipment Failure Analysis , Reproducibility of Results , Sensitivity and Specificity , Staining and Labeling , Surface PropertiesABSTRACT
OBJECTIVE: To evaluate the efficacy of color Doppler sonography in detecting possible differences in blood flow patterns and B-mode sonographic characteristics between malignant and benign cervical lymph nodes. PATIENTS AND METHODS: During a period of 10 months, the palpable cervical lymph nodes of 39 patients were prospectively evaluated with B-mode and color Doppler sonography. The echogenity, contour, ratio of longitudinal diameter to the transverse diameter and the presence of a hilus were evaluated by B-mode sonography. Capsullary and intranodal arterial flow rates were measured and maximal systolic, end-diastolic, mid-systolic flow velocities with pulsatility, resistivity and acceleration indices were obtained. Final diagnosis was established by excisional biopsy (n:34) and clinical follow-up (n:5). RESULTS: The lymph nodes in 20 cases were malignant and in 19 cases were benign. The B-mode contour characteristics and presence of a hilus in malignant and benign lymph nodes were statistically significant (P < 0.05), but there were no significant differences between the ratio of longitudinal diameter to the transverse diameter (P > 0.05), echogenity (P > 0.05) and the diameters of lymph nodes (P > 0.05). Flow patterns were obtained in 14 malignant (70%) and 10 benign (52.6%) cases. The maximal systolic, end diastolic, mid-systolic flow velocities and pulsatility, resistivity, acceleration indices did not differ statistically (P > 0.05). CONCLUSION: In the differentiations of benign and malignant cervical lymph nodes, the B-mode and color Doppler sonography are limited methods and can not replace biopsy.