There is renewed interest in land-based cultivation of green and red seaweeds for production of food ingredients and novel bioproducts under controlled conditions. A common practice is tank cultivation with continuous seawater exchange. A dynamic process model was developed to predict seaweed biomass productivity as a function of seawater exchange rate in land-based aquaculture systems, where dissolved inorganic carbon (DIC) and macronutrients for photosynthetic biomass production are supplied principally by the seawater inflow. The dynamic model predicted DIC concentration, limiting nutrient concentration, biomass density, areal biomass productivity, and pH vs time profiles during the light and dark phases of the photoperiod. The differential material balance equations posed by the model were coupled to a multiplicative Monod equation that quantified the effect of DIC and limiting macronutrient (nitrate) concentrations on specific growth rate. Model predictions were compared to biomass productivity vs. seawater exchange rate data for tank cultivation of green macroalgae (Ulva species) and red macroalgae (Palmaria, Gracilaria species) available in the literature. This model predicted the asymptotic effect of seawater exchange rate and biomass productivity. Furthermore, model predictions revealed that diminished biomass productivity at seawater exchange rates of less than 5 day−1 are due to macronutrient limitations on growth, not DIC limitation, motivating the use of integrated multitrophic aquaculture systems to supply nitrate and phosphate to inlet flow seawater above ambient levels. Overall, the model can be used to determine the optimal seawater exchange rate for a desired biomass productivity and provide predictive capability for future engineering design and economic analysis.

The red seaweed Devaleraea mollis, commonly known as Pacific dulse, is a sustainable source of healthy food, food ingredients, and plant-based proteins. Land-based aquaculture of red seaweed typically employ tumble culture systems, where compressed air is delivered to the bottom of the tank to provide gas exchange and promote mixing. However, aeration is a potentially costly process because compressed air must be bubbled into the liquid, and power is required to drive the air compressor. In this study, fundamental relationships between aeration rate, biomass productivity, and aeration power consumption were developed for tumble tank cultivation of the red seaweed Pacific dulse under CO2-replete growth conditions. The biomass productivity (g biomass L-1 d-1) of D. mollis in tumble culture was measured over seven weekly harvest cycles over a range of aeration rates (0.086-0.684 L air L-1 liquid min-1) for fine-bubble (1-5 mm) and coarse-bubble (2-3 cm) aerators, and then correlated to the CO2 transfer rate (CO2-TR, mmol CO2 L-1 h-1). The CO2-TR consolidated aeration rate, CO2 partial pressure, boundary layer diffusion, and gas sparger characteristics (bubble size, interfacial area) into a single parameter. This analysis required measurements of the gas-to-liquid mass transfer coefficient (kLa) for estimation of CO2-TR, and pressure drop across the gas diffuser for aeration power consumption. CO2-replete biomass productivity required a CO2-TR that was three times the CO2 demand. For fine-bubble aeration, both CO2-TR and aeration power consumption were higher than for coarse-bubble aeration over the range of aeration rates tested. However, when the aeration rate needed to achieve CO2-replete biomass productivity was approached, fine-bubble aeration required less energy consumption due to lower aeration requirement. The optimum was achieved at an aeration rate of 0.26 L air L-1 culture min-1 using fine-bubble aeration, which provided an areal biomass productivity of 490 g FW m- 2 d-1 (fresh mass) or 32 g AFDW m- 2 d-1 (ash-free dry mass), at an aeration energy power requirement of 1.5 kWh/kg FW (22 kWh/kg AFDW). Overall, this study showed that aeration systems can easily limit biomass productivity and result in high aeration energy consumption per kg of biomass produced if the aeration processes are not thoughtfully considered. The key tradeoff was that aeration energy consumption increased significantly as CO2-replete biomass productivity was approached. Therefore, optimization would require the use of an aerator system that provides the best possible kLa and lowest pressure drop at the lowest possible aeration rate.

Diatoms are single-celled algae that biosynthesize cell walls of biogenic silica called "frustules" that are intricately patterned at the submicron- and nanoscale. In this study, we amplified the intrinsic luminescent properties of antibody-functionalized diatom biosilica frustules for enhanced, label-free, photoluminescence (PL) detection of immunocomplex formation. It was hypothesized that metabolically doped GeO centers in antibody-functionalized diatom biosilica would enhance PL emission associated with nucleophilic immunocomplex formation. Germanium (Ge) was metabolically inserted into the frustule biosilica by two-stage cell cultivation of the centric diatom Cyclotella sp. The biosilica frustules were isolated by hydrogen peroxide treatment and thermally annealed to convert Ge oxides in the biosilica (0.4 wt% Ge) to luminescent GeO centers. The Ge-doped biosilica frustules were then functionalized with Rabbit Immunoglobulin G (IgG). Upon immunocomplex formation with its complimentary antigen goat anti-Rabbit IgG, the Ge-oxide doped, antibody-functionalized frustule biosilica increased the intensity of PL emission by a factor of 2.6 relative to immunocomplex formation by antibody-functionalized frustule biosilica without Ge. It is proposed that the luminescent GeO centers in the Ge-oxide doped frustule biosilica were more sensitive to radiative recombination than luminescent silanol groups in frustule biosilica without Ge, resulting in a higher PL emission upon immunocomplex formation.

The last 20 years has seen rapid expansion of sustainable energy deployment in the European Union (EU) and the United States (U.S.) that is driving the demand for trained professionals. An engineering degree with coursework in sustainable energy systems is a desirable initial qualification. However, engineering students should also appreciate the societal and environmental impacts of the sustainable energy transition. Furthermore, since the sustainable energy transition is a global endeavor, an international perspective is needed. The sustainable energy engineering course described in this paper taught students the scientific and engineering principles underlying the major types of emerging sustainable energy technologies from a chemical engineering perspective. The technical content served as context for comparing renewable energy deployment in the EU country of Austria with the U.S. The broader impacts (societal and environmental) of renewable energy deployment were then illustrated through student presentations. Survey results showed that students gained understanding of the engineering fundamentals underlying these renewable energy systems and challenges of their deployment in Austria and the U.S. Therefore, a unique outcome of this course was that students gained an international perspective on the expansion of sustainable energy systems needed to secure a low-carbon energy future.

New approaches are needed for land-based cultivation of macrophytic red algae that reduce costly aeration requirements for biomass suspension and enable high-density cultivation. The goal of this study was to demonstrate the high-density cultivation of the carbohydrate-rich macrophytic red alga Gracilaria vermiculophylla on vertical arrays of panels deployed in an open channel raceway configuration similar to those developed for mass cultivation of microalgae. A clonal culture of G. vermiculophylla, consisting of branched, cylindrical thallus tissues of 8-10 cm length, was mechanically blended using a Waring blender into 2-3 cm fragments and then fluidically injected onto a 3 mm polypropylene mesh support. Immobilized G. vermiculophylla mesh panels were spaced 6.5 cm apart and aligned parallel to flowing seawater medium at nominal bulk velocity of 20 cm s(-1) in a 100 L raceway pond of 20 cm liquid depth. This raceway was equipped with real-time measurement of CO2 concentration in the inlet and outlet gas for determination of CO2 uptake dynamics. Specific rates for CO2 uptake became saturated at 8000 ppm CO2. To match CO2 demand by the biomass under nutrient-replete conditions at 21 degrees C, the inlet gas CO2 was increased from 1000 to 4000 ppm (day 7-14), and then to 8000 ppm (day 14-23) at 0.010 L gas L-1 liquid min(-1) gas flow. Over the 23 day cultivation, biomass on the panel increased by a factor of 48, with final biomass loading exceeding 10 kg FW m(-2) panel area, and cumulative CO2 capture of 65%. The cumulative average areal productivity within the panel zone of the raceway exceeded 60 g AFDW m(-2) day(-1), and final biomass density nearing 7.2 g AFDW L-1 (47 g FW L-1) was achieved after 23 days. Overall, these outcomes demonstrate the potential for land-based raceway cultivation of clonal red macroalgae of present and future commercial significance.

This study assessed the productivity of the red alga Palmaria mollis (Pacific dulse) plantlets immobilized on a vertical array of mesh panels in aerated tank culture. Biomass productivity rates based on panel surface area, as well as areal productivity based on liquid surface area, were assessed at different panel spacing intervals in a greenhouse with continuous illumination (500 µmol photons m−2 s−1) and weekly f/2 nutrient enrichment, as well as outdoors with natural solar irradiance and continuous natural seawater inflow at 10 exchanges per day. The temperature of all cultivations averaged 12 °C. For greenhouse cultivation in 60-L aerated tanks (0.8 L air L−1 culture min−1), as the panel spacing decreased from 12 to 6 cm, biomass productivity per panel on the 30 × 30 cm panels decreased from to 165 to 112 g FW (fresh weight) m−2 panel day−1, due to reduced growth associated with light attenuation by fronds crowding into the space between panels. However, areal productivity was maintained at 17–18 g AFDW (ash-free dry weight) m−2 day−1, because twice as many panels were present in the same liquid surface area. Areal productivity for tumble culture was statistically higher at 21 g AFDW m−2 day−1. For outdoor cultivation in an 850-L tank with 30 × 80-cm panels, the same trends were observed, but the best panel productivity was 72 g FW m−2 panel day−1 at 25 cm spacing, and the best areal productivity was 8.0 g AFDW m−2 day−1 at 6-cm spacing. Overall, the immobilization of P. mollis on a vertical array of mesh panels offers a modular and flexible cultivation platform, but further optimization is needed to maximize productivity.

This study investigated the feasibility of cultivating clonal red macroalgae on a porous mesh support. Clonal plantlets of macrophytic red alga Ochtodes secundiramea served as the model culture system. The morphology of O. secundiramea is defined by highly-branched shoot tissues. Plantlets were mechanically blended (8000 rpm, 7 s) and allowed to recover for 7 days prior to immobilization. A 2.0 g FW L-1 slurry of 3 mm branched shoot tissues was injected onto a fiberglass mesh with 1.6 mm openings in 0.5 s bursts at pressure of 8 bar and nominal fluid velocity of 1.7 m s-1. Each burst deposited a 25 mg shoot tissue cluster onto the mesh. Clusters were placed on a rectangular pitch at decreasing intervals of 20, 12, 8, and 6 mm (contiguous layer) in order to increase the inoculation density. A parallel array of upright, plantlet-inoculated mesh panels was positioned at the base of an aerated, externally illuminated tank, and enriched artificial seawater medium flowed across both sides of each panel. Biomass growth was linear with time, and increased by a factor of 10 over the 28 day cultivation period. Increasing panel inoculation density from 49 to 114 g FW m- 2 panel mesh area doubled panel biomass productivity from 14.5 to 28.6 g FW m- 2 day-1. Immobilized plantlets proliferated outward across the mesh surface to form a highly branched, densified shoot tissue mass about 1.5 cm thick, and final panel biomass coverage exceeding 3.0 kg FW per m2 of active panel area was achieved. Overall, the outcomes of this study demonstrate that pressurized fluid injection of clonal plantlets onto a mesh surface, and the subsequent proliferation of the shoot tissues on the mesh to form a contiguous panel, offers potential for the future automation and intensification of red macroalgal biomass production.

New approaches are needed to automate and intensify the cultivation of commercially important red macroalgae. For example, cultivation of Gracilaria vermiculophylla on vertically stacked panels, deployed in raceway circulation tanks or in the open ocean, may enable process intensification. A scalable process for panel inoculation is a first step toward this end. Clonal plantlets of G. vermiculophylla were mechanically blended (1000 rpm, 5 s) into tissue fragments of 2 cm nominal size, deposited on a 3-mm polypropylene mesh sheet, and then sprayed with a pressurized water jet at 4.5 bar in 0.1 s bursts with average velocity of 13 m s−1. The force of the water jet pushed the 1 mm diameter thallus tissue fragments into the mesh openings, securing the plantlet to the mesh support. Gracilaria vermiculophylla test panels (7 cm per side) were placed in an upright orientation, with rising air bubbles providing fluid motion over the panel surface. During cultivation at saturation light intensity in nutrient-replete medium, near-exponential growth was sustained over 42 days at a specific growth rate of 8–9% per day, identical to the freely suspended thallus tissues. The tissue fragments proliferated over the panel surface and extended outward from the panel surface, ultimately creating a loose mat of tissue nearly 8–10 cm in thickness and biomass loadings exceeding 3000 g FW per m2 of panel surface. The steps used to prepare the G. vermiculophylla panels can be automated, and dense arrays of stationary G. vermiculophylla panels cultivated under defined current flow offer future potential for process intensification.

In vivo functionalization of diatom biosilica frustules by genetic manipulation requires careful consideration of the overall structure and function of complex fusion proteins. Although we previously had transformed Thalassiosira pseudonana with constructs containing a single domain antibody (sdAb) raised against the Bacillus anthracis Sterne strain, which detected an epitope of the surface layer protein EA1 accessible in lysed spores, we initially were unsuccessful with constructs encoding a similar sdAb that detected an epitope of EA1 accessible in intact spores and vegetative cells. This discrepancy limited the usefulness of the system as an environmental biosensor for B. anthracis. We surmised that to create functional biosilica-localized biosensors with certain constructs, the biosilica targeting and protein trafficking functions of the biosilica-targeting peptide Sil3T8 had to be uncoupled. We found that retaining the ER trafficking sequence at the N-terminus and relocating the Sil3T8 targeting peptide to the C-terminus of the fusion protein resulted in successful detection of EA1 with both sdAbs. Homology modeling of antigen binding by the two sdAbs supported the hypothesis that the rescue of antigen binding in the previously dysfunctional sdAb was due to removal of steric hindrances between the antigen binding loops and the diatom biosilica for that particular sdAb.

Diatoms are single‐celled algae that biologically fabricate nanostructured silica shells with ordered pore arrays called frustules that resemble a 2D photonic crystal. A monolayer of Pinnularia frustules isolated from cell culture is deposited on a glass substrate and then conformally coated with silver nanoparticles (AgNPs) to serve as a nanostructured thin film for ultrathin layer chromatography (UTLC). Malachite green and Nile red are resolved in toluene mobile phase and the separated analytes are profiled micro‐Raman spectroscopy, where plasmonic AgNPs provide surface‐enhanced Raman scattering (SERS). The AgNP‐diatom frustule monolayer improves SERS detection of malachite green by an average factor of 1.8 ± 0.1 over the plasmonic AgNP layer on glass. Analysis of hot spots on the AgNP‐diatom frustule monolayer reveals that nearly 20% of the SERS active area intensifies the SERS signal at least tenfold over the SERS signal for AgNP on glass. Diatom‐SERS enhancement is attributed to guided‐mode resonances of the Raman laser source, which in turn further enhances the localized surface plasmonic resonance from AgNPs. Overall, the AgNP‐diatom frustule monolayer thin film is a new functional material that uniquely enables separation of analytes by UTLC, quantitative SERS detection of separated analytes, and photonic enhancement of the SERS signals.

Marine diatoms are photosynthetic microalgae that make a unique biosilica cell wall called the frustule that possesses intricate pore arrays ordered at the submicron and nanoscale. Diatoms are responsible for a nearly 40 percent of carbon fixation in the ocean. There are a broad spectrum of carbon compounds produced by marine diatoms, such as proteins, lipids, and carbohydrates. This chapter describes the biosynthesis and the fiber structure of extracellular chitin nanofibers. Marine diatoms fix inorganic carbon by photosynthesis and make glucose-6-phosphate through carbohydrate metabolism. Chitin nanofiber formation occurs in three steps: polymerization, crystallization and extrusion. The polymerization step occurs in the chitinpockets that are located below each fultoportulae. The crystallization process occurs in the chitin pocket between different chitin chains that interact with each other, creating inter-chain and intra-chain hydrogen bonds.

In recent years, researchers have successfully applied diatom biosilica to molecular detection platforms including Surface-Enhanced Raman Scattering (SERS) optofluidic sensors that are currently capable of detecting a variety of biological and chemical molecules at concentrations as low as 10−10 M. This study investigates the feasibility of an SERS device that couples the sensing and pumping capabilities of diatom biosilica thin films by determining flow rate limitations and stability. In this paper, we quantify the ability of porous diatom biosilica thin films to continuously pump deionized (DI) water from a reservoir via wicking flow by utilizing the strong capillary forces of the porous film coupled with evaporation. Our microfluidic device is comprised of a narrow horizontal reservoir fixed to a horizontal capillary whose end contacts a diatom biosilica film. Flow rates were controlled by altering the size and/or temperature of the biosilica porous film, determined by tracking the liquid meniscus displacement in the reservoir, and correlated with a modified laminar boundary-layer model. System stability was observed by tracking flow rates over the course of a given experiment, image analysis of the meniscus contacting the film, and a flow duration study. We found that for untreated DI water bubbles begin to form in the capillary tube at temperatures above 40 °C, but degassed water remains stable at temperatures of 90 °C and below. The pumping capabilities of the films ranged from 0.11 to 10.46 µL/min, matched theoretical predictions, demonstrated stable flow trends, and maintained flow for over 48 h.

Surface-enhanced Raman scattering (SERS) has started to attract attention in vapor sensing; however, practical applications require shorter response time and better sensitivity. Herein, we report a facile multiscale SERS substrate for trace-level detection of vapors using a portable Raman spectrometer through the synergistic integration of biologically fabricated diatom photonic crystals and gold-silica core-shell nanoparticles. The multiscale substrate is composed of (1) a micrometer-scaled, 3-dimensional, diatom biosilica frustule enabling efficient vaporsubstrate interaction for rapid sensing, (2) periodic pores, on the order of 100 nm, inducing plasmonic-photonic coupled resonances for enhanced SERS signals, (3) gold nanoparticle cores, with a diameter on the order of 10 nm, contributing plasmonic field enhancements, and (4) porous 1 nm thick silica core-shells enabling analyte vapor adsorption and concentration. The combination of the hierarchal, multiscale features results in a SERS substrate capable of rapid and sensitive detection of target vapors in air. The multiscale substrates functionality is characterized using the polycyclic aromatic hydrocarbon pyrene, and the contribution from each scale is verified by using a stagnant vapor chamber. The sensor equilibrates in only 3 min, and detection is achieved down to 1 ppm. The sensor is then applied to the detection of explosive 2,4-dinitrotoluene vapor below 100 ppb in an airflow chamber to replicate practical detection conditions, achieving detection in under 3 min at room temperature and under 1 min when heated. This work successfully demonstrates detection of explosive vapor and represents a significant advancement toward widespread vapor sensing via SERS.

This study compared the growth of Laminaria saccharina female gametophyte filamentous cell suspension cultures in a stirred-tank photobioreactor under batch and fed-batch nutrient addition modes over a 48-day cultivation period. Cultures were grown on GP2 artificial seawater medium (0.75 mM nitrate, N:P = 16:1) at pH 8.3 without iron or copper. Total equivalent nutrient loadings ranged from 0.5X to 9.1X GP2 for batch cultivation and 1.3X to 10.4X GP2 for fed-batch cultivation at delivery rates of 0.0067–0.16 mmol N L−1 day−1 based on nitrate. The multicellular, L. saccharina filamentous clumps were dispersed to nominal size of 100 μm by mechanical blending (~ 16,000 rpm, 5 s) prior to inoculation. Fed-batch addition of all nutrients enhanced biomass productivity by a factor of two over a batch cultivation process at equivalent total nutrient loadings in a stirred-tank photobioreactor. Peak productivity through fed-batch cultivation was 57 mg DCW L−1 day−1, and average final biomass densities exceeded 1800 mg DCW L−1, vs. 30 mg DCW L−1 day−1 and 800–900 mg DCW L−1 for batch cultivation. However, there was a limit to biomass productivity enhancement at cumulative nutrient loadings greater than 3X GP2 that was not the result of insufficient CO2 or light delivery. It is suggested that the formation of large, multicellular clumps approaching 1-mm diameter during stirred-tank cultivation may have ultimately reduced biomass productivity during fed-batch cultivation under nutrient-replete conditions. Therefore, future bioreactor processing strategies might consider mechanical blending to disperse the filament clumps during the cultivation process.

We synthesized hybrid photonic crystal-plasmonic mesocapsules using diatom biosilica with in-situ growth silver nanoparticles. The mesocapsules achieved near single-molecule sensitivity for optofluidic SERS sensing with five orders of magnitude higher than colloidal nanoparticles.

Diatoms are a group of single-celled photosynthetic algae that use biochemical pathways to bio-mineralize and self-assemble three-dimensional photonic crystals with unique photonic and micro- & nano-fluidic properties. In recent years, diatom biosilica has been used in surface-enhanced Raman scattering (SERS) based optofluidic sensors for detection of a variety of chemical and biological molecules. In this paper, we present a study to develop a microfluidic pumping system using super-hydrophilic diatom thin films. The desire to develop such a system stems from the requirement to create a low-cost, self-powered microfluidic pumping system that can sustain a continuous flow over an extended period of time. The diatom biosilica acts not only as the driving force behind the flow, but also serves as ultra-sensitive SERS substrates that allows for trace detection of various molecules. Liquid is drawn from a reservoir to the tip of a 150μm inner diameter capillary tube positioned directly over the diatom film. A thin and long horizontal reservoir is used to prevent flooding on the diatom film when the liquid is initially drawn to the diatom film through a capillary tube from the reservoir. The connection of the meniscus from the capillary to the film was maintained from a horizontal reservoir for a recorded time of 20 hours and 32 minutes before the partially filled reservoir emptied. Flow rates of 0.38, 0.22 and 0.16μL/min were achieved for square biosilica thin films of 49mm2, 25mm2, and 9mm2 at a temperature of 63°F and 45% relative humidity respectively. A temperature-controlled system was introduced for the 49mm2 substrate and flow rates of 0.60, 0.82, 0.93, and 1.15μL/min were observed at 72, 77, 86, and 95°F at 21% relative humidity respectively. More testing and analysis will be performed to test the operation limits of the proposed self-powered microfluidic system.

Tetrahydrocannabinol (THC) is the main active component in marijuana and the rapid detection of THC in human body fluid plays a critical role in forensic analysis and public health. Surface-enhanced Raman scattering (SERS) sensing has been increasingly used to detect illicit drugs; however, only limited SERS sensing results of THC in methanol solution have been reported, while its presence in body fluids, such as saliva or plasma, has yet to be investigated. In this article, we demonstrate the trace detection of THC in human plasma and saliva solution using a SERS-active substrate formed by in situ growth of silver nanoparticles (Ag NPs) on diatom frustules. THC at extremely low concentration of 1 pM in plasma and purified saliva solutions were adequately distinguished with good reproducibility. The SERS peak at 1603 cm-1 with standard deviation of 3.4 cm-1 was used for the evaluation of THC concentration in a methanol solution. Our SERS measurement also shows that this signature peak experiences a noticeable wavenumber shift and a slightly wider variation in the plasma and saliva solution. Additionally, we observed that THC in plasma or saliva samples produces a strong SERS peak at 1621 cm-1 due to the stretching mode of O-C═O, which is related to the metabolic change of THC structures in body fluid. To conduct a quantitative analysis, principal component analysis (PCA) was applied to analyze the SERS spectra of 1 pM THC in methanol solution, plasma, and purified saliva samples. The maximum variability of the first three principal components was achieved at 71%, which clearly denotes the impact of different biological background signals. Similarly, the SERS spectra of THC in raw saliva solution under various metabolic times were studied using PCA and 98% of the variability is accounted for in the first three principal components. The clear separation of samples measured at different THC resident times can provide time-dependent information on the THC metabolic process in body fluids. A linear regression model was used to estimate the metabolic rate of THC in raw saliva and the predicted metabolic time in the testing data set matched well with the training data set. In summary, the hybrid plasmonic-biosilica SERS substrate can achieve ultrasensitive, near-quantitative detection of trace levels of THC in complex body fluids, which can potentially transform forensic sensing techniques to detect marijuana abuse.

Optical biosensing has achieved remarkable levels of sensitivity and has enabled early detection of various toxins and biomarkers. Fluorescence spectroscopy is among the most common and powerful optical detection techniques, capable of single molecule detection. This is done by exciting the sample using a light source, collecting the fluorescence light inherent in the sample or on a reporter molecule, and measuring the fluorescence spectrum using a spectrometer. This modality is effective for multiplex sensing as full spectral data is acquired. However, fluorescence spectroscopy requires multiple measurements at multiple points to achieve a representative sampling of a sensor. Fluorescence imaging is a detection modality similar to fluorescence spectroscopy, but replaces the spectrometer with an imager such as a camera thus reducing cost and complexity. Imaging allows data acquisition at multiple points in a large area of your sensor in a single measurement making it a more efficient sensing method but does not acquire spectral data. Both fluorescence sensing modalities have been shown to be very powerful in pristine laboratory settings but when the equipment or measurement area are not ideal, additional enhancement is needed. This can be achieved by implementing a sensing substrate capable of enhancing fluorescence signals to practical detection levels. Diatoms are unicellular marine organisms that grow a biosilica shell called a frustule. These frustules are porous with nanostructured patterns and represent naturally occurring photonic crystals which are known to enhance excitation and emission of fluorophores. In addition to the optical enhancements of diatoms, the large surface area allows for large numbers of analytes to aggregate making fluorescence signals stronger. In this work, we employ naturally occurring photonic crystal diatoms to create a sensor capable of enhancing the fluorescence of a standard sandwich immunoassay. Using this sensor, we achieved detection down to 10-16 M using fluorescence spectroscopy and 10-15 M for fluorescence imaging. These represent a 100× and 10× enhancement for the two respective detection modalities over equivalent, non-diatom sensors. This highlights the capability of our sensor to enhance fluorescence optical signals and its potential to be used in point-of-care biosensing applications.

A photonic crystal-enhanced fluorescence imaging immunoassay biosensor is capable of detecting NT-proBNP as a cardiovascular biomarker at various concentrations. Utilizing machine-learning algorithms, we create a predictive model for the analyte quantification. © 2019 The Author(s)