We report an aptasensor for homogeneous ochratoxin A (OTA) detection based on luminescence resonance energy transfer (LRET). This system uses upconversion nanoparticles (UCNPs), such as NaYF4:Yb3+, Er 3+, as the donor. The aptamer includes the optimum-length linker (5-mer-length DNA) and OTA-specific aptamer sequences. Black hole quencher 1 (BHQ1), as the acceptor, was modified at the 3' end of the aptamer sequence. BHQ1 plays as a quencher in LRET aptasensor and shows absorption at 543 nm, which overlaps with well the emission of the UCNPs. When OTA is added, the BHQ1-labeled OTA aptamer was folded due to the formation of the G-quadruplex-OTA complex, which induced the BHQ1 close to the UCNPs. Consequently, resonance energy transfer between UCNPs (donor) and BHQ1 (acceptor) enables quenching of upconversion luminescence signals under laser irradiation of 980 nm. Our results showed that the LRET-based aptasensor allows specific OTA analysis with a limit of detection of 0.03 ng/mL. These results demonstrated that the OTA in diverse foods can be detected specifically and sensitively in a homogeneous manner.
In this study, C-reactive protein (CRP) was detected by monitoring of LSPR shift promoted by precipitation of 4-chloro-1-naphthol (4-CN). The precipitation occurred by horseradish peroxide (HRP) catalyst which is modified at CRP-detection antibody utilized in sandwich enzyme-linked immunosorbent assay (ELISA) on gold nano bipyramid (GNBP) substrate. Due to 4-CN precipitates which are located nearby the surface of GNBP, local refractive index (RI) and molecular density were greatly increased. This phenomenon eventually induced strong spectral red-shift of absorption band of GNBP. An excellent linear relationship (R2=0.9895) between the LSPR shift and CRP concentration was obtained in the range from 100 pg/mL to 100 ng/mL and limit of detection (LOD) was reached to 87 pg/mL.
Localized surface plasmon resonance (LSPR) of metal nanoparticles makes red-shift of extinction wavelength with an increase in the refractive index at the surface of the metal nanoparticles. Since biomolecules bound to the metal nanoparticle’s surface induce refractive index change, biosensing based on LSPR effect can be possible by monitoring scattering or absorption spectrum changes. Generally, however, conventional method detects ensemble averaged LSPR signal of a huge number of metal nanoparticles. Here, we have constructed a dark-field spectral imaging microscope in order to monitor the scattering spectra of individual metal nanoparticles, simultaneously. Gold nanorod (GNR) and aptamer are employed to detect ochratoxin A (OTA) related to a carcinogenic illness. An aptamer-target binding mechanism promotes wavelength shift of extinction spectra due to refractive index change within sensing volume of GNR by structural change of aptamer. A number of GNRs can be identified in a dark-field LSPR image, simultaneously. A typical spectrum of a GNR exhibits red-shift after target binding of molecules and OTA detection is extended to the very low concentration of 1 pM level.
Cerenkov luminescence (CL) is generated when a charged particle moves faster than the speed of light in dielectric media. Recently CL imaging becomes an emerging technique with the use of radioisotopes. However, due to relatively weak blue light production and massive tissue attenuation, CL has not been applied widely. Therefore, we attempted to shift the CL emission to more near infrared (NIR) spectrum for better tissue penetration by using Cerenkov Radiation Energy Transfer (CRET). Gold nanoclusters were conjugated with NIR dye molecules (AuNc-IR820 and AuNc-ICG) to be activated with ultraviolet light. We found optimal conjugate concentrations of AuNc-NIR conjugates by spectroscopy system to generate maximal photon emission. When exposed by ultraviolet light, the emission of NIR light from the conjugates were verified. In quantitative analysis, AuNc-NIR conjugates emit brighter light signal than pure AuNc. This result implies that NIR fluorescent dyes (both IR820 and ICG) can be excited by the emission from AuNc. Following the above baseline experiment, we mixed F-18 fluorodeoxyglucose (F-18 FDG) radioisotope to the AuNc- NIR conjugates, to confirm NIR emission induced from Cerenkov radiation. Long pass filter was used to block Cerenkov luminescence and to collect the emission from AuNc-NIR conjugates. Instead of one long exposure imaging with CCD, we used multiple frame scheme to eliminate gamma radiation strike in each frame prior to combination. In summary, we obtained NIR emission light from AuNc-NIR conjugated dyes that is induced from CL. We plan to perform in vivo small animal imaging with these conjugates to assess better tissue penetration.
Recent advances in nanotechnology have led to improvements in numerous fields, including biomedical research and health care systems. Successful application of nanotechnology in the areas of biosensing, imaging, and spectroscopy is expected to revolutionize medical research and diagnostics, ultimately leading to unprecedented improvement in healthcare. This special section presents 10 papers covering a wide range of research topics on optical biosensing, nanomaterial-based biological imaging and phototherapy, and nanofabrication technologies.
Hyper-Rayleigh Scattering (HRS) is a second-order nonlinear optical process in which the scattered light can be detected
at the second harmonic wavelength of the input laser beam. Due to its incoherent nature, it can be observed from metal
nanoparticles whose size is much smaller than the wavelength. Its sensitive response to the nanoparticle aggregation can
be used as a powerful diagnostic tool for the detection of biological target molecules. Many previous bio-sensing
applications of HRS have used gold nanoparticles as their sensing platform due to easy synthesis and functionalization of
them. Here, we demonstrate that the aggregation of silver nanoparticles induced by poly-L-lysine molecules can generate
much higher HRS than that from gold nanoparticle aggregates when using a Ti:Sapphire femtosecond laser. In spite of
several drawbacks of silver nanoparticle system regarding the nonlinear response to target concentration and the
difficulty of surface functionalization compared to the gold nanoparticle system, much higher HRS from silver
nanoparticles can be definitely useful for the sensitive detection of very small amount of target molecules.
In this study, we used a Complementary Metal Oxide Semiconductor (CMOS) image sensor with immobilizing
antibodies on its surface to detect human cytokines, which are activators that mediate intercellular communication
including expression and control of immune responses. The CMOS image sensor has many advantages over the Charge
Couple Device, including lower power consumption, operation voltage, and cost. The photodiode, a unit pixel
component in the CMOS image sensor, receives light from the detection area and generates digital image data. About a
million pixels are embedded, and size of each pixel is 3 x 3 μm. The chemiluminescence reaction produces light from
the chemical reaction of luminol and hydrogen peroxide. To detect cytokines, antibodies were immobilized on the
surface of the CMOS image sensor, and a sandwich immunoassay using an HRP-labeled antibody was performed. An
HRP-catalyzed chemiluminescence reaction was measured by each pixel of the CMOS image sensor. Pixels with
stronger signals indicated higher cytokine concentrations; thus, we were able to measure human interleukin-5 (IL-5) at
femtomolar concentrations.
Herein, we have developed a label-free and homogeneous fluorescence resonance energy transfer (FRET) immunoassay
for the detection of neopterin (NPT), which is an early and valuable biochemical marker of cellular immunity. Owing to
intrinsic fluorescence properties of antibody and NPT, anti-NPT antibody (anti-NPT) and analyte played roles as the
respective donor and acceptor in the FRET immunoassay. As the concentration of NPT increases, the fluorescence
intensity at ~350 nm decreases owing to the formation of increasing amounts of the anti-NPT/NPT complex in which
FRET takes place. The assay system was found to display a high specificity and a low detection limit (0.14 ng mL-1) for
NPT. A practical application of the FRET immunoassay system was demonstrated by its use in the detection of NPT in
spiked human serum samples. The observations made in these efforts show that the homogeneous FRET immunoassay
strategy, which requires a simple sample preparation procedure, serves as a powerful tool for the rapid and sensitive
quantitative determination of NPT.
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