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Nano Focus Photonic-crystal nanolasers shown to be highly sensitive

ove over, ELISA. While the MEnzyme-Linked ImmunoSorbent Assay has long been one of the most popu- lar ways of detecting and quantifying the presence of antibodies or antigens in solu- tion, nanolasers may be poised to share the spotlight on the stage. Using a photonic-crystal nanolaser developed by their team, engineering professor Toshihiko Baba and colleagues at Yokohama National University’s Department of Electrical and Computer Schematic of nanolaser biosensor and mode profi le. (Top right): Modal profi le Engineering in Japan have demonstrated without nanoslot; mode is most intense at the nanoslot position. (Bottom): GaInAsP slab the utility of their device as a disposable of quantum wells on InP substrate. Periodic holes, which form a , are sensor for several biomedical applica- modifi ed to form the central slot (top left), which is the main part of the sensor. Credit: Toshihiko Baba/Yokohama National University. tions. Their experiments, presented in MRS Communications (DOI: 10.1557/ mrc.2015.73) show promise for detect- ing targets including proteins, endotoxins, Functionalizing the nanolaser with a sensing of other molecules. Endotoxins and DNA sequences. molecule known to bind with the target are detected rapidly; gel formation dur- Enzyme immunoassays determine molecule provides biological specifi city. ing reaction with a reagent is the current, whether body fl uids contain proteins re- To detect a protein, this means fi xing an but slow, method. Baba’s team detected lated to certain diseases. Contemporary antibody to the nanolaser surface. the wavelength shift due to gelation faster immunoassays often require expensive “We can detect a smaller amount of than is possible with standard assays. For fl uorescent labels and complicated proce- protein than the limit of ELISA. This DNA, they showed that hybridization to dures. Furthermore, their detection limit means we can use a lower concentration a probe attached to the nanolaser is de- can be insuffi cient for many important of protein as a biomarker for severe dis- tectable through changes in both wave- proteins. Now, Baba aims to provide “an eases, which offers a higher diagnostic length and laser emission intensity. This immunosensor beyond the current stan- probability,” adds Baba. eliminates the need for traditional labels dard technology,” exploiting the nanola- Proteins in body fl uids help to identify in detecting specifi c sequences. ser’s sensitivity to changes in refractive particular diseases. However, existing Other photonics-based methods of index and surface charge. tests are limited by detection sensitivity. label-free protein sensing show promise “Our interest is using the nanolaser If lower concentrations could be detect- too, but they face the challenge of distin- for immunosensing. But it has the po- ed, diagnoses could be improved. guishing signal from noise caused by non- tential to detect toxins, cells, and chemi- For prostate cancer screening, current specifi c binding and other contamination. cals. However, photonic sensors are not tests for detecting the prostate-specifi c The nanolaser sensor’s suitability results [yet] available for medical applications. antigen are useful at the threshold, but from a combination of selectivity for tar- ELISA has been superior to those re- not at lower levels. Experiments using get proteins, minimal sample damage, ported so far,” says Baba. the nanolaser in blood proxy bovine se- repeatability, low cost, and experimental The Yokohama group fabricated a rum albumin suggest that detection could simplicity. nanolaser from an indium gallium arsenide be achieved below sub-picomolar (pM = “The study implies that we can have phosphide wafer with a lattice of holes 10–12M) concentrations, well below the large sensitivity, and also scalability. But comprising the photonic crystal separated range needed for post-surgical monitor- specifi city is still dependent on the func- by an air layer from an indium phosphide ing. Additionally, Baba’s team detected tionalization, not solely on the laser,” says substrate. Shifting several holes resulted the antibody-antigen reaction of a pro- Arka Majumdar, an electrical engineer and in a nanolaser cavity that lases at ~1550 tein biomarker for Alzheimer’s disease physicist at the University of Washington, nm when pumped with light at 980 nm. at 10 pM concentration in cultured cells who was not involved in the study. As the of the fl uid in the and in lymphocites, two orders of mag- Baba plans to continue the investiga- cavity changes upon immersion in solution nitude better than ELISA. tion, to deliver superior stability and quan- containing various concentrations of pro- The nanolaser’s sensitivity to a vari- tifi cation for each target biomolecule. teins, so does the nanolaser wavelength. ety of surface modifi cations also allows Rachel Berkowitz

Downloaded8 MRSfrom BULLETIN https://www.cambridge.org/core • VOLUME 41 • JANUARY. 2016IP address: • www.mrs.org/bulletin 170.106.33.14, on 26 Sep 2021 at 14:40:47, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/mrs.2015.317