Ultrafast Mid-Infrared Nanoscopy of Strained Vanadium Dioxide Nanobeams

Long regarded as a model system for studying insulator-to-metal phase transitions, the correlated electron material vanadium dioxide (VO2) is now finding novel uses in device applications. Two of its most appealing aspects are its accessible transition temperature (∼341 K) and its rich phase diagram. Strain can be used to selectively stabilize different VO2 insulating phases by tuning the competition between electron and lattice degrees of freedom. It can even break the mesoscopic spatial symmetry of the transition, leading to a quasiperiodic ordering of insulating and metallic nanodomains. Nanostructuring of strained VO2 could potentially yield unique components for future devices. However, the most spectacular property of VO2--its ultrafast transition--has not yet been studied on the length scale of its phase heterogeneity. Here, we use ultrafast near-field microscopy in the mid-infrared to study individual, strained VO2 nanobeams on the 10 nm scale. We reveal a previously unseen correlation between the local steady-state switching susceptibility and the local ultrafast response to below-threshold photoexcitation. These results suggest that it may be possible to tailor the local photoresponse of VO2 using strain and thereby realize new types of ultrafast nano-optical devices.

Evaluation of focused sentinel lymph node RT-qPCR screening for micrometastases with the use of the Maruyama computer program

Background

In this preliminary study, we investigated the sensitivity and specificity of reverse transcriptase (RT)-qPCR lymph node (LN) metastases detection, the accuracy of intraoperative dye navigation, and the incidence of micrometastasis (MM) detection with this protocol, compared to other published studies.

Methods

A total of 23 patients were enrolled in the study. The first stained LN was analyzed using RT-qPCR for carcinoembryonic antigen (CEA) and cytokeratin 20 (CK-20) expression, as markers for MM involvement. The Maruyama computer program was used to determine the most likely first metastatic site. These results were compared with the actual staining patterns to evaluate whether the first draining LN was extracted. We analyzed the correlations between MM and tumor characteristics. The incidence of MM detected with the present method was compared to other studies, as markers of the accuracy of the present protocol.

Results

At 35 threshold cycles, the RT-qPCR had a negative predictive value of 100 % and a positive predictive value of 83.3 %. MM were detected in 4 out of 14 node-negative patients (28.6 %). The extracted sentinel LN coincided in 76.9 % of cases with the most probable first metastatic LN predicted by the Maruyama program. MM were found more frequently in these ‘high-risk’ LNs. Significant differences were found in the Lauren’s histological type distribution and the age distribution among the MM-positive and MM-negative groups.

Conclusion

Our preliminary results confirm that RT-qPCR is an accurate method of MM detection, that the dye navigation enables the determination of the first draining LN, and that the incidence of MM detection with this focused sentinel LN protocol is comparable to other studies.

Evaluation of a focused sentinel lymph node protocol in node-negative gastric cancer patients

BACKGROUND/AIMS

A specific preoperative work-up was used to access a limited number of high-risk lymph nodes with RT-qPCR for micrometastatic sentinel lymph node involvement. We validated our protocol with IHC screening for micrometastases and long-term survival analysis.

METHODOLOGY

From the 32 patients included 22 were node-negative patients. With a specific preoperative protocol sentinel lymph nodes (1-2 per patient) were extracted for further RT-qPCR analysis for CEA and CK20 expression. In 10 patients from the study group, the remaining lymph nodes around the extracted sentinel lymph node from the first compartment were additionally screened using IHC for missed micrometastases.

RESULTS

Micrometastases were detected in seven of 22 (31.8%) node-negative patients. RT-qPCR identified micrometastases in four of 10 haematoxylin-eosin-negative lymph nodes (40%), and in three of eight IHC negative lymph nodes (37.5%). The cumulative 3-year survival for the study group was 80.8%. The 3-year survival in the RT-qPCR-negative group was 90%, compared with 66.7% in the RT-qPCR-positive group (p=0.289).

CONCLUSIONS

Encouraged by these results, we will include more patients in our focused sentinel lymph node protocol. With a refinement of our method, we believe the focused sentinel lymph node protocol can be implemented for intraoperative tailoring of extent of lymphadenectomy.