A diphoton event display from the CMS collaboration (Image: CERN)
The Rencontres de Moriond in La Thuile Italy, are traditionally the most important meeting place for particle physicists in winter. After last year’s restart of the Large Hadron Collider at unprecedented energy, and as Rencontres de Moriond celebrate their 50th anniversary, physicists gathered last week with much interest for the electroweak session, to look at the latest results from the LHC experiments. Analyses presented during the week included measurements of the Higgs boson using last year’s LHC 13 TeV data, an eagerly anticipated update on diphoton resonances search, precision measurements of Standard Model processes, and new searches for supersymmetric particles and dark matter.
The week started with many results in the heavy flavours area, where one of the main highlights came from the LHCb experiment. Looking at their data, physicists of the LHCb collaboration could not spot any evidence for the existence of X(5568)– a tetraquark particle candidate recently reported by Fermilab’s DZero collaboration. LHCb and DZero collaborations will work together to investigate further, following this interesting outcome.
ATLAS also presented their full Run 1 result of a search for the extremely rare decay of a Bs meson to a muon pair.
The decay was observed by CMS and LHCb in 2014 from a combination of their datasets. The ATLAS analysis resulted in a signal that is smaller than expected, but still compatible with the Standard Model.
After a lot of hard work to calibrate and characterize the data collected, both ATLAS and CMS provided an update on an intriguing result first presented last December: a small excess above background in the diphoton channel near a mass of 750 GeV, which could mean, if confirmed, the existence of a new unexpected particle.
With refined analysis, the “bump” in the data is still there, but the statistical significance of the result still remains too low to be conclusive. Physicists must wait for the imminent restart of data collection before they can investigate further, as the LHC has been in its winter pause over the last weeks. Physicists will have to wait for summer conferences, such as ICHEP 2016 in Chicago, to possibly get excited again.
For more highlights from Moriond, see the latest from the ATLAS, CMS and LHCb experiments and from Symmetry Magazine.
Sensing biological molecules on chip has become an irreplaceable component of modern medical diagnostics. Blood, saliva, urine, and other bodily fluids can be tested for the presence of viruses, bacteria, and other harmful agents using numerous methods that typically rely on chemical reactions between the biomolecule and a reagent. Recently, other biosensing methods are being tested, in particular those that rely on optical readout, which can provide a fast and reliable sensing platform.
Surface plasmon resonances (SPR) have surfaced as an interesting candidate among the optical sensing methods. SPR is a term that describes the interaction of light with metal nanoparticles. Light of a specific color is concentrated around the nanoparticle with high intensity in a small volume, enabling detection of minute concentrations of molecules near the nanoparticle, down to the level of single molecules or cells. The specific wavelength (color) of light that excites the SPR is defined by the nanoparticle shape and size.
Adding a graphene layer below the metal nanoparticles increases sensitivity of SPR sensors, but graphene also often plays the role of protein or molecule immobilizer. The typical metal used for SPR is gold, due to its favorable optical properties (low losses). However, the metal atoms in gold nanoparticles tend to distort the crystal structure of graphene, lowering material quality and decreasing SPR sensitivity.
Now a team of researchers in Madrid has grown gallium nanoparticles on Graphenea’s CVD graphene for SPR biosensing. Gallium, a group III metal, forms weaker bonds than gold with graphene, causing almost no distortion of the crystal structure. The device showed a strong SPR response and the researchers demonstrated sensing of organic molecules. The research was published in “physica status solidi b”, a leading journal for solid state physics.
Gallium was deposited on graphene with thermal evaporation and annealing, a simple, low cost, and reproducible method. SPR was measured with ellipsometry, commonly used to measure optical properties of thin films and nanoparticles. Interestingly, the research showed that nanoparticles grown on graphene tend to have a narrower size distribution compared to those grown on a bare SiO2 substrate. A narrow size distribution is favorable for selectivity of SPR sensors.
To show sensing behavior, the researchers functionalized the surface with 3,3′-dithiodipropionic acid di(N-succinimidyl ester) (DTSP), a crosslinking reagent. DTSP is commonly used to link organic biomarkers to surfaces, such as gold. Sensing operation was demonstrated by a clear shift in plasmonic resonance after adding DTSP. Furthermore, it was shown that the sensor that included graphene worked better than one without graphene.
