Porous silicon microcavities based photonic barcodes

Spatially Resolved Organic Whispering-Gallery-Mode Hetero-Microrings for High-Security Photonic Barcodes

Whispering-gallery-mode (WGM) microcavities featuring distinguishable sharp peaks in a broadband exhibit enormous advantages in the field of miniaturized photonic barcodes. However, such kind of barcodes developed hitherto are primarily based on microcavities wherein multiple gain medias were blended into a single matrix, thus resulting in the limited and indistinguishable coding elements. Here, a surface tension assisted heterogeneous assembly strategy is proposed to construct the spatially resolved WGM hetero-microrings with multiple spatial colors along its circular direction. Through precisely regulating the charge-transfer (CT) strength, full-color microrings covering the entire visible range were effectively acquired, which exhibit a series of sharp and recognizable peaks and allow for the effective construction of high-quality photonic barcodes. Notably, the spatially resolved WGM hetero-microrings with multiple coding elements were finally acquired through heterogeneous nucleation and growth controlled by the directional diffusion between the hetero-emulsion droplets, thus remarkably promoting the security strength and coding capacity of the barcodes. The results would be useful to fabricate new types of organic hierarchical hybrid WGM heterostructures for optical information recording and security labels.

Faithful Fabrication of Biocompatible Multicompartmental Memomicrospheres for Digitally Color-Tunable Barcoding

Barcodes have attracted widespread attention, especially for the multiplexed bioassays and anti-counterfeiting used toward medical and biomedical applications. An enabling gas-shearing approach is presented for generating 10-faced microspherical barcodes with precise control over the properties of each compartment. As such, the color of each compartment could be programmatically adjusted in the 10-faced memomicrospheres by using pregel solutions containing different combinations of fluorescent nanoparticles. During the process, three primary colors (red, green, and blue) are adopted to obtain up to seven merged fluorescent colors for constituting a large amount of coding as well as a magnetic compartment, capable of effective and robust high-throughput information-storage. More importantly, by using the biocompatible sodium alginate to construct the multicolor microspherical barcodes, the proposed technology is likely to advance the fields of food and pharmaceutics anti-counterfeiting. These remarkable properties point to the potential value of gas-shearing in engineering microspherical barcodes for biomedical applications in the future.

Optical-resonance-assisted generation of super monodisperse microdroplets and microbeads with nanometer precision

Droplets with predefined sizes have been controllably produced at the tip of a micro-capillary immersed in an external fluid while tracking the high Q-factor whispering gallery modes (WGM). The modes were fitted to a model to give precise real-time size measurement, which was used as a feedback to control the pressure in the capillary and the release of the droplet from the capillary when it reached the target size. In this way a dispersion of highly monodisperse droplets anywhere in the size range from 5 μm to 50 μm were produced. To fabricate solid beads, the droplets were made from a liquid photopolymer and were later polymerized with UV light. The polymerized beads showed long term stability. The diameter of the generated oil droplets and polymerized microbeads could be reproduced with a standard deviation of 1.1 nm and 20 nm, respectively. Overall, the demonstrated method improves the size precision by three and two orders of magnitude for microdroplets and microbeads, respectively, compared to standard production methods such as reported in microfluidics. Encoding of short words and numbers has been demonstrated by producing three beads with predefined sizes. The stored information has been read from the emitted spectrum.

Organic micro/nanoscale materials for photonic barcodes

This review summarizes recent advances in micro/nanoscale photonic barcodes based on organic materials from the aspects of diverse optical encoding techniques.

Modular assembly of plasmonic core-satellite structures as highly brilliant SERS-encoded nanoparticles

Herein, we present a fabrication approach that produces homogeneous core-satellite SERS encoded particles with minimal interparticle gaps (<2-3 nm) and maximum particle loading, while positioning the encoding agents at the gaps. Integration of plasmonic building blocks of different sizes, shapes, compositions, surface chemistries or encoding agents is achieved in a modular fashion with minimal modification of the general synthetic protocol. These materials present an outstanding optical performance with homogeneous enhancement factors over 4 orders of magnitude as compared with classical SERS encoded particles, which allows their use as single particle labels.

Barcoded point-of-care bioassays

Barcoded bioassays are ready to promote bioanalysis and biomedicine toward the point of care.

Spectral reading of optical resonance-encoded cells in microfluidics

The ability to label individual cells is useful for single-cell-level studies of complex cellular interactions and heterogeneity. Optically readable cell labeling is attractive as it can be investigated non-invasively and repeatedly at high speeds. Here, we demonstrate the feasibility of large-scale cell barcoding and identification using fluorescent polystyrene microbeads loaded into cells. Intracellular beads with different diameters in a range of 5 to 12 μm generate spectrally distinguished features or barcodes. A microfluidic chip was used to measure fluorescence resonance peaks emitted from individual cells. An algorithm comparing the peak wavelengths to a reference barcode library allowed barcode identification with high accuracy. This work provides a guideline to increase the number of unique identifiers and reduce various false-positive and false-negative errors.

Covert Photonic Barcodes Based on Light Controlled Acidichromism in Organic Dye Doped Whispering-Gallery-Mode Microdisks

Photonic barcodes with a small footprint have demonstrated a great value for multiplexed high-throughput bioassays and tracking systems. Attempts to develop coding technology tend to focus on the generation of featured barcodes both with high coding capacity and accurate recognition. In this work, a strategy to design photonic barcodes is proposed based on whispering-gallery-mode (WGM) modulations in dye-doped microdisk resonant cavities, where each modulated photoluminescence spectrum constitutes the fingerprint of a corresponding microdisk. The WGM-based barcodes can achieve infinite encoding capacity through tuning the dimensions of the microdisks. These photonic barcodes can be well disguised and decoded based on the light controlled proton release and acidichromism of the organic materials, which are essential to fulfill the functions of anti-counterfeiting, information security, and so on. The results will pave an avenue to new types of flexible WGM-based components for optical data recording and security labels.

Observation of strongly enhanced photoluminescence from inverted cone-shaped silicon nanostructures. [corrected]

Silicon nanowires (SiNWs) attached to a wafer substrate are converted to inversely tapered silicon nanocones (SiNCs). After excitation with visible light, individual SiNCs show a 200-fold enhanced integral band-to-band luminescence as compared to a straight SiNW reference. Furthermore, the reverse taper is responsible for multifold emission peaks in addition to the relatively broad near-infrared (NIR) luminescence spectrum. A thorough numerical mode analysis reveals that unlike a SiNW the inverted SiNC sustains a multitude of leaky whispering gallery modes. The modes are unique to this geometry and they are characterized by a relatively high quality factor (Q ~ 1300) and a low mode volume (0.2 < (λ/n_eff)³ < 4). In addition they show a vertical out coupling of the optically excited NIR luminescence with a numerical aperture as low as 0.22. Estimated Purcell factors F_p ∝ Q/V_m of these modes can explain the enhanced luminescence in individual emission peaks as compared to the SiNW reference. Investigating the relation between the SiNC geometry and the mode formation leads to simple design rules that permit to control the number and wavelength of the hosted modes and therefore the luminescent emission peaks.

Silicon particles as trojan horses for potential cancer therapy

BACKGROUND

Porous silicon particles (PSiPs) have been used extensively as drug delivery systems, loaded with chemical species for disease treatment. It is well known from silicon producers that silicon is characterized by a low reduction potential, which in the case of PSiPs promotes explosive oxidation reactions with energy yields exceeding that of trinitrotoluene (TNT). The functionalization of the silica layer with sugars prevents its solubilization, while further functionalization with an appropriate antibody enables increased bioaccumulation inside selected cells.

RESULTS

We present here an immunotherapy approach for potential cancer treatment. Our platform comprises the use of engineered silicon particles conjugated with a selective antibody. The conceptual advantage of our system is that after reaction, the particles are degraded into soluble and excretable biocomponents.

CONCLUSIONS

In our study, we demonstrate in particular, specific targeting and destruction of cancer cells in vitro. The fact that the LD50 value of PSiPs-HER-2 for tumor cells was 15-fold lower than the LD50 value for control cells demonstrates very high in vitro specificity. This is the first important step on a long road towards the design and development of novel chemotherapeutic agents against cancer in general, and breast cancer in particular.

Nanostructural Engineering of Nanoporous Anodic Alumina for Biosensing Applications

Modifying the diameter of the pores in nanoporous anodic alumina opens new possibilities in the application of this material. In this work, we review the different nanoengineering methods by classifying them into two kinds: in situ and ex situ. Ex situ methods imply the interruption of the anodization process and the addition of intermediate steps, while in situ methods aim at realizing the in-depth pore modulation by continuous changes in the anodization conditions. Ex situ methods permit a greater versatility in the pore geometry, while in situ methods are simpler and adequate for repeated cycles. As an example of ex situ methods, we analyze the effect of changing drastically one of the anodization parameters (anodization voltage, electrolyte composition or concentration). We also introduce in situ methods to obtain distributed Bragg reflectors or rugate filters in nanoporous anodic alumina with cyclic anodization voltage or current. This nanopore engineering permits us to propose new applications in the field of biosensing: using the unique reflectance or photoluminescence properties of the material to obtain photonic barcodes, applying a gold-coated double-layer nanoporous alumina to design a self-referencing protein sensor or giving a proof-of-concept of the refractive index sensing capabilities of nanoporous rugate filters.

Band-gap engineering by molecular mechanical strain-induced giant tuning of the luminescence in colloidal amorphous porous silicon nanostructures

A novel approach for producing and tuning the emission of a colloidal dispersion of amorphous porous silicon nanoparticles via controlled oxidation and disorder increase.

Electrochemical engineering of hollow nanoarchitectures: pulse/step anodization (Si, Al, Ti) and their applications

Hollow nanoarchitectured materials with straight channels play a crucial role in the fields of renewable energy, environment and biotechnology due to their one-dimensional morphology and extraordinary properties. The current challenge is the difficulty on tailoring hollow nanoarchitectures with well-controlled morphology at a relatively low cost. As a conventional technique, electrochemistry exhibits its unique advantage on machining nanostructures. In this review, we present the progress of electrochemistry as a valuable tool in construction of novel hollow nanoarchitectures through pulse/step anodization, such as surface pre-texturing, modulated, branched and multilayered pore architectures, and free-standing membranes. Basic principles for electrochemical engineering of mono- or multi-ordered nanostructures as well as free-standing membranes are extracted from specific examples (i.e. porous silicon, aluminum and titanium oxide). The potential of such nanoarchitectures are further demonstrated for the applications of photovoltaics, water splitting, organic degradation, nanostructure templates, biosensors and drug release. The electrochemical techniques provide a powerful approach to produce nanostructures with morphological complexity, which could have far-reaching implications in the design of future nanoscale systems.

Porous silicon microcavities: synthesis, characterization, and application to photonic barcode devices

We have recently developed a new type of porous silicon we name as porous silicon colloids. They consist of almost perfect spherical silicon nanoparticles with a very smooth surface, able to scatter (and also trap) light very efficiently in a large-span frequency range. Porous silicon colloids have unique properties because of the following: (a) they behave as optical microcavities with a high refractive index, and (b) the intrinsic photoluminescence (PL) emission is coupled to the optical modes of the microcavity resulting in a unique luminescence spectrum profile. The PL spectrum constitutes an optical fingerprint identifying each particle, with application for biosensing.In this paper, we review the synthesis of silicon colloids for developing porous nanoparticles. We also report on the optical properties with special emphasis in the PL emission of porous silicon microcavities. Finally, we present the photonic barcode concept.

Photoluminescent enzymatic sensor based on nanoporous anodic alumina

Herein, we present a smart enzymatic sensor based on nanoporous anodic alumina (NAA) and its photoluminescence (PL) in the UV-visible range. The as-produced structure of NAA is functionalized and activated in order to perform the enzyme immobilization in a controlled manner. The whole process is monitored through the PL spectrum and each stage is characterized by an exclusive barcode, which is associated with the PL oscillations. This characteristic property allows us to calculate the change in the effective optical thickness that takes place after each stage. This makes it possible to accurately detect and quantify the immobilized enzyme within the NAA structure. Finally, the NAA geometry (i.e., the pore length and its diameter) is optimized to improve the enzyme immobilization and its detection inside the pores. This enzymatic sensor can give quick and accurate measurements of enzyme levels, what is crucial in clinical enzymology to prevent and detect diseases at their primary stage.

Tunable Fabry-Pérot interferometer based on nanoporous anodic alumina for optical biosensing purposes

Here, we present a systematic study about the effect of the pore length and its diameter on the specular reflection in nanoporous anodic alumina. As we demonstrate, the specular reflection can be controlled at will by structural tuning (i.e., by designing the pore geometry). This makes it possible to produce a wide range of Fabry-Pérot interferometers based on nanoporous anodic alumina, which are envisaged for developing smart and accurate optical sensors in such research fields as biotechnology and medicine. Additionally, to systematize the responsiveness to external changes in optical sensors based on nanoporous anodic alumina, we put forward a barcode system based on the oscillations in the specular reflection.

Nanoporous anodic alumina barcodes: toward smart optical biosensors

Toward a smart optical biosensor based on nanoporous anodic alumina (NAA): by modifying the pore geometry in nanoporous anodic alumina we are able to change the effective medium at will and tune the photoluminescence of NAA. The oscillations in the PL spectrum are converted into exclusive barcodes, which are useful for developing optical biomedical sensors in the UV-Visible region.