We investigated sequence-specific and simultaneous microRNA (miRNA) detections by surface plasmon resonance (SPR) imaging measurements on SPR chips possessing an Au spot array modified with probe DNAs based on a miRNA-detection-selective SPR signal amplification method. MiRNAs were detected with the detection limit of the attomole level by SPR imaging measurements for different miRNA concentrations on a single chip. SPR signals were enhanced based on a combination process of sequence-specific hybridization of the miRNA to the probe DNAs, extension reaction of polyadenine (poly(A)) tails by poly(A) polymerase, binding of a ternary complex of T 30-biotin/horseradish peroxidase (HRP)-biotin/streptavidin to the poly(A) tails, and the oxidation reaction of tetramethylbenzidine (TMB) on the HRP by providing a blue precipitate on the surface. This process sequence-specifically and dramatically amplified the SPR signals. This is a simple, cost-effective, and feasible signal amplification method based on the organic compound TMB instead of metal nanoparticles.
Determining black hole masses and accretion rates with better accuracy and precision is crucial for understanding quasars as a population. These are fundamental physical properties that underpin models of active galactic nuclei. A primary technique to measure the black hole mass employs the reverberation mapping of low-redshift quasars, which is then extended via the radius-luminosity relationship for the broad-line region to estimate masses based on single-epoch spectra. An updated radius-luminosity relationship incorporates the flux ratio of optical Fe ii to Hβ ($\equiv \mathcal {R}_{\rm Fe}$) to correct for a bias in which more highly accreting systems have smaller line-emitting regions than previously realized. In this current work, we demonstrate and quantify the effect of using this Fe-corrected radius-luminosity relationship on mass estimation by employing archival data sets possessing rest-frame optical spectra over a wide range of redshifts. We find that failure to use a Fe-corrected radius predictor results in overestimated single-epoch black hole masses for the most highly accreting quasars. Their accretion rate measures (LBol/LEdd and $\dot{\mathscr {M}}$), are similarly underestimated. The strongest Fe-emitting quasars belong to two classes: high-z quasars with rest-frame optical spectra, which given their extremely high luminosities, require high accretion rates, and their low-z analogs, which given their low black holes masses, must have high accretion rates to meet survey flux limits. These classes have mass corrections downward of about a factor of two, on average. These results strengthen the association of the dominant Eigenvector 1 parameter $\mathcal {R}_{\rm Fe}$ with the accretion process.
We describe the development and performance of a new type of optical sensor suitable for registering the binding/dissociation of nanoscopic particles near a gold sensing surface. The method shares similarities with surface plasmon resonance microscopy but uses a completely different optical signature for reading out binding events. This new optical read-out mechanism, which we call confined optical field enhanced fluorescence emission (Cofefe), uses pulsed surface plasmon polariton fields at the gold/liquid interface that give rise to confined optical fields upon binding of the target particle to the gold surface. The confined near-fields are sufficient to induce two-photon absorption in the gold sensor surface near the binding site. Subsequent radiative recombination of the electron-hole pairs in the gold produces fluorescence emission, which can be captured by a camera in the far-field. Bound nanoparticles show up as bright confined spots against a dark background on the camera. We show that the Cofefe sensor is capable of detecting gold and silicon nanoparticles, as well as polymer nanospheres and sub-μm lipid droplets in a label-free manner with average illumination powers of less than 10 μW/μm.
N-Isopropylacrylamide-based hydrogel nanoparticles (HNPs) that incorporate 30 mer single-stranded DNA (ssDNA) oligonucleotides were synthesized and characterized with single-nanoparticle surface plasmon resonance imaging (SPRI) microscopy, dynamic light scattering, transmission electron microscopy, and fluorescence measurements. The synthesized HNPs had an averaged diameter of 230 nm and exhibited a large (5−10×) increase in the average single-nanoparticle SPRI refractive index (Δ% R NP ), as compared with HNPs without DNA. A combination of SPRI and fluorescence measurements was used to measure the uptake of approximately 20 000 complementary ssDNA into each HNP, resulting in a Langmuir isotherm adsorption coefficient of 4.89 × 10 8 M −1 . Single-nanoparticle SPRI measurements also showed that approximately 35% of the incorporated ssDNA was accessible for both hybridization uptake and enzymatic hydrolysis using exonuclease I. We attribute the presence of an inactive ssDNA population in the nanoparticle to a combination of acrylamide Michael addition reactions with adenine, cytosine, and guanine nucleotides, as well as the possible formation of self-complementary secondary structures in the polymerized ssDNA.
We present spectroscopic measurements for 226 sources from the Gemini Near Infrared Spectrograph–Distant Quasar Survey (GNIRS-DQS). Being the largest uniform, homogeneous survey of its kind, it represents a flux-limited sample (m i ≲ 19.0 mag, H ≲ 16.5 mag) of Sloan Digital Sky Survey (SDSS) quasars at 1.5 ≲ z ≲ 3.5 with a monochromatic luminosity ( ) at 5100 Å in the range of 1044–1046 erg s−1. A combination of the GNIRS and SDSS spectra covers principal quasar diagnostic features, chiefly the C iv λ1549, Mg ii λλ2798, 2803, Hβ λ4861, and [O iii] λλ4959, 5007 emission lines, in each source. The spectral inventory will be utilized primarily to develop prescriptions for obtaining more accurate and precise redshifts, black hole masses, and accretion rates for all quasars. Additionally, the measurements will facilitate an understanding of the dependence of rest-frame ultraviolet–optical spectral properties of quasars on redshift, luminosity, and Eddington ratio, and test whether the physical properties of the quasar central engine evolve over cosmic time.
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