The use of phycobiliproteins as fluorescent labels in immunoassay

Properties and potential applications of bioconjugates of R-phycoerythrin with Ag° or CdS nanoparticle synthesized in its tunnel cavity: A review

Green synthesis is a promising method for the preparation of nanoparticles (NPs) due to its simplicity, low cost, low toxicity, and environmental friendliness. Biosynthesized NPs exhibit multifunctional activity, good biocompatibility, and higher anticancer and antibacterial activity compared to chemically synthesized NPs. R-phycoerythrin, a photosynthetic light-harvesting pigment of protein nature (M.w. 290 kDa), is an attractive platform for the synthesis of small sizes NPs due to its structural features, non-toxicity, water solubility. Photosensitive bioconjugates of R-phycoerythrin with NPs were prepared by synthesizing Ag° and CdS NPs in tunnel cavities of R-phycoerythrin (3.5 × 6.0 nm) isolated from the red seaweed Callithamnion rubosum. The review is devoted to the physical processes and chemical reactions that occur in the native protein macromolecule of a complex structure during the synthesis of a NP in its cavity. The influence of Ago and CdS NPs on the electronic processes caused by the absorption of photons, leading to reversible and irreversible changes in R-phycoerythrin has been analyzed. Properties of R-phycoerythrin bioconjugates Ag° and CdS with NPs combined with the literature data suggest potential applications of Ag°⋅PE and CdS⋅PE bioconjugates for cancer diagnosis, treatment, and monitoring as well as for realizing theranostic strategy in the future. The use of these bioconjugates in anticancer therapy may have synergistic effects since both R-phycoerythrin and NPs induce cancer cell death.

Development of Spectral Imaging Cytometry

Spectral flow cytometry is a new technology that enables measurements of fluorescent spectra and light scattering properties in diverse cellular populations with high precision. Modern instruments allow simultaneous determination of up to 40+ fluorescent dyes with heavily overlapping emission spectra, discrimination of autofluorescent signals in the stained specimens, and detailed analysis of diverse autofluorescence of different cells-from mammalian to chlorophyll-containing cells like cyanobacteria. In this paper, we review the history, compare modern conventional and spectral flow cytometers, and discuss several applications of spectral flow cytometry.

The increasing role of structural proteomics in cyanobacteria

Cyanobacteria, also known as blue–green algae, are ubiquitous organisms on the planet. They contain tremendous protein machineries that are of interest to the biotechnology industry and beyond. Recently, the number of annotated cyanobacterial genomes has expanded, enabling structural studies on known gene-coded proteins to accelerate. This review focuses on the advances in mass spectrometry (MS) that have enabled structural proteomics studies to be performed on the proteins and protein complexes within cyanobacteria. The review also showcases examples whereby MS has revealed critical mechanistic information behind how these remarkable machines within cyanobacteria function.

Study of fluorescence spectroscopy and molecular mechanisms for the interaction of Hg2+ ions and R-phycoerythrin from marine algae (Porphyra yezoensis)

Heavy metal is a worldwide hazardous material, and many efforts were made to detect them sensitively and selectively. R-phycoerythrin (R-PE), a marine fluorescent protein, is abundant in red algae and participates in photosynthesis. In this work, the fluorescence spectroscopy and molecular mechanism of Hg2+ ions and R-PE were further explored through fluorescence spectrum measurements, time-resolved fluorescence lifetimes, peak fitting of Fourier transform infrared spectroscopy, and molecular docking simulation in this study. It was proved by fluorescent spectrum measurements that Hg2+ ions could lead to static fluorescence quenching. Besides, the interaction was a spontaneous and exothermic process driven by hydrogen bond and Van der Waals (VDW) force. Importantly, Hg2+ ions bound to 78LYS and 82CYS on the α chain and 73CYS and 82CYS on the β chain, which resulted in the structural changes of the peptide chain and affected the secondary structure contents of R-PE. This study further explained the effect of Hg2+ ions on marine fluorescent protein R-PE.

Triple quantitative detection of three inflammatory biomarkers with a biotin-streptavidin-phycoerythrin based lateral flow immunoassay

Quantified inflammatory biomarkers are effective clinical strategy for correct and reasonable drug treatment. In the study, a triple lateral flow immunoassay (triple LFIA) had firstly been developed for specific and simultaneous detection of three pivotal inflammatory biomarkers (PCT, CRP and SAA) via biotin-streptavidin-phycoerythrin signal amplification system in one strip. The developed triple LFIA adopted phycoerythrin (PE) as chromophore to eliminate auto-fluorescence interference from plasma biomolecules and anti-PE mAb as single control line to reduce the nonspecific adsorption, which featured particular advantages in high sensitivity and specificity in a large range of analyte concentrations with the LODs of 0.106 ng/mL for PCT, 0.345 μg/mL for CRP and 3.112 μg/mL SAA, respectively. And the linear quantitative detection ranges were from 0.106 to 100 ng/mL, from 0.345 to 200 μg/mL, and from 3.112 to 200 μg/mL, respectively. Compared to commercial chemiluminescence immunoassay method, the correlations for tested PCT, CRP and SAA in 108 clinical samples were 0.989, 0.987 and 0.988, respectively. In summary, we had proposed a rapid and accurate plasma detection to measure inflammation factors, which facilitated the clinical value to achieve precise treatment.

Construction of fluorescent logic gates for the detection of mercury(II) and ciprofloxacin based on phycocyanin

Chemical pollutants such as heavy metals and antibiotics in the environment pose a huge threat to humans and animals. Our studies have demonstrated that the fluorescence of phycocyanin showed quenching responses towards both mercury (Hg2+) and ciprofloxacin (CIP), which acted in accordance with the "OR" molecular logic gate. In order to discriminate Hg2+ and CIP in application scenarios, cysteine (Cys) was utilized to design another "INHIBIT" logic gate, in which Hg2+ and Cys were the two inputs. Thus, an intelligent biosensor with dual-target identification capacity was successfully developed by using a fluorescent natural protein in an ingenious logic gate system.

Phycobiliprotein as fluorescent probe and photosensitizer: A systematic review

Phycobiliprotein is a natural product with many biological activities in various seaweeds. Phycobiliproteins have been widely used for anti-oxidation, anti-tumor, anti-inflammatory and immune-enhancing activities as a functional factor. Phycobiliproteins with high purity are considerably more expensive than common. To provide with a systematic, deep and detailed information about those features of phycobiliproteins, we performed a relatively comprehensive analysis on structural composition, the application of phycobiliproteins in the fields of fluorescent probe and photodynamic therapy in this report.

R-Phycoerythrin from Colaconema formosanum (Rhodophyta), an Anti-Allergic and Collagen Promoting Material for Cosmeceuticals

R-phycoerythrin (R-PE), a pigment complex found in red algae, was extracted and purified from a newly identified red alga, Colaconema formosanum, and its bioactivities were examined. It was revealed that R-PE treatment resulted in high cell viability (>70%) to the mammalian cell lines NIH-3T3, RBL-2H3, RAW264.7, and Hs68, and had no effect on cell morphology in NIH-3T3 cells. Its suppression effect was insignificant on the production of IL-6 and TNF-α in lipopolysaccharides-stimulated RAW264.7 cells. However, calcium ionophore A23187-induced β-hexosaminidase release was effectively inhibited in a dose-dependent manner in RBL-2H3 cells. Additionally, it was revealed to be non-irritating to bionic epidermal tissues. Notably, procollagen production was promoted in Hs68 cells. Overall, the data revealed that R-PE purified from C. formosanum exhibits anti-allergic and anti-aging bioactivities with no observed consequential toxicity on multiple mammalian cell lines as well as epidermal tissues, suggesting that this macromolecule is a novel material for potential cosmetic use.

Ultrasensitive and selective detection of Hg2+ using fluorescent phycocyanin in an aqueous system

Hg²⁺ toxicity is one of the most common chemical poisonings that occurs mainly from drinking polluted water. In the current work, Phycocyanin (PC) was exploited as a fluorescent sensor for sensitive and selective detection of Hg²⁺ in an aqueous system. PC-Hg²⁺ interaction was monitored using a spectro-fluorometer under different buffered solutions at pH values of 6,7,8,9, or 10 above the isoelectric point of PC (5.18). A remarkable decrease of PC fluorescence intensity was observed under Tris-buffer at pH 6 upon the addition of increasing Hg²⁺ concentrations (1-120 nM). Under the maintained experimental conditions, the current sensor showed a good linear relationship with R² = 0.9971 and a limit of detection as low as 0.7 nM was achieved. In addition, a notable selectivity of Hg²⁺ over other nine heavy metals (Cu^2+, Zn^2+, Pb²⁺, Mg^2+, Mn⁴⁺, Li⁺, Fe^3+, Co²⁺, and Al³⁺) was achieved in the presence of 120 nM of each metal. Moreover, the current fluorescent detection assay was also tested in real samples of pond water, and recoveries as well as relative standard deviations within the acceptable limits were recorded.

Efficient Purification of R-phycoerythrin from Marine Algae (Porphyra yezoensis) Based on a Deep Eutectic Solvents Aqueous Two-Phase System

R-phycoerythrin (R-PE), a marine bioactive protein, is abundant in Porphyra yezoensis with high protein content. In this study, R-PE was purified using a deep eutectic solvents aqueous two-phase system (DES-ATPS), combined with ammonium sulphate precipitation, and characterized by certain techniques. Firstly, choline chloride-urea (ChCl-U) was selected as the suitable DES to form ATPS for R-PE extraction. Then, single-factor experiments were conducted: the purity (A₅₆₅/A₂₈₀) of R-PE was 3.825, and the yield was 69.99% (w/w) under optimal conditions (adding 0.040 mg R-PE to ChCl-U (0.35 g)/K₂HPO₄ (0.8 g/mL, 0.5 mL) and extracting for 20 min). The sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) results revealed that the purified R-PE contained three main bands. One band was presented after purification in native-PAGE. The UV-vis spectra showed characteristic absorption peaks at 495, 540, and 565 nm. R-PE displayed an emission wavelength at 570 nm when excited at 495 nm. All spectra results illustrated that the structure of R-PE remained unchanged throughout the process, proving the effectiveness of this method. Transmission electron microscope (TEM) showed that aggregation and surrounding phenomena were the driving forces for R-PE extraction. This study could provide a green and simple purification method of R-PE in drug development.

A novel monoclonal antibody against human B7-1 protects against chronic graft-vs.-host disease in a murine lupus nephritis model

Lupus nephritis (LN) is the most common complication that causes mortality in patients with systemic lupus erythematosus. The B7-1/B7-2 and CD28/cytotoxic T-lymphocyte associated protein 4 co-stimulatory pathway serves a key role in autoimmune disease and organ transplantation. The aim of the present study was to generate and characterize a monoclonal antibody (mAb; clone 4E5) against human B7-1 and to investigate its potential use for the treatment of LN. The results demonstrated that the 4E5 mAb was successfully generated and able to recognize both human and mouse B7-1. After injection of this mAb into a mouse model with chronic graft-vs.-host disease (cGVHD)-induced lupus-like disease, the expression of CD21, CD23, CD80 and CD86 on B220⁺ B-cells in the spleen, and the concentrations of serum autoantibodies and urine protein, were decreased. Direct immunofluorescence analysis of the kidneys revealed that immunofluorescence of immune complex deposits was weaker in the 4E5-treated mice and electron microscopy analyses of renal tissues indicated that pathological injury of the kidneys of 4E5-treated mice was decreased compared with that in the model control mice. The results of the present study demonstrated that inhibition of the B7-1/CD28 co-stimulatory signaling pathway with the 4E5 mAb may represent a promising strategy to decelerate the progression of LN that is induced by cGVHD with potential for use in the treatment of other autoimmune diseases.

Fluorescence Signal Amplification by Using β-Galactosidase for Flow Cytometry; Advantages of an Endogenous Activity-Free Enzyme

We previously proposed using a hydrolysis enzyme for fluorescent signal amplification in flow cytometric detection of antigen proteins, which was named the catalyzed reporter penetration (CARP) method. In this method, antigen proteins are labeled with enzyme-modified antibodies, and then fluorophore-modified substrates stain cells by penetrating the cell membrane upon hydrolysis of the substrate. We proved the concept by using alkaline phosphatase (AP) as the hydrolysis enzyme. However, a required prior inactivation process of endogenous AP activity on the cell surface risked disrupting recognition of antigen proteins by antibodies. In this report, the CARP method was extended to β-galactosidase (β-gal) as an amplification enzyme, which circumvented the requirement of an initial inactivation process because endogenous β-gal activity on the surface of examined cells was found to be negligible. The substrate structure for β-gal was optimized and used for the CARP method. The CARP method showed significantly higher fluorescent signals than a conventional method using fluorophore-modified antibodies. Moreover, the degree of amplification of the fluorescence signal was higher for antigens with low expression levels, showing that the CARP method is a suitable signal amplification method over current conventional approaches.

Signal amplification in flow cytometry for cell surface antigen analysis

Signal enhancing systems have been introduced to enable detection of cell surface antigens by flow cytometry. Cell surface antigens are important targets that describe the function and lineage of cells. Although flow cytometry is an effective tool for analysing cell surface antigens, this technique has poor sensitivity, which prohibits the detection of many important antigens on cell membranes. Thus, signal amplification is essential for developing practical tools for evaluating cell surface antigens by flow cytometry. Using a bright fluorophore or fluorescent polymer incorporated into antibodies is a straightforward strategy to improve flow cytometry sensitivity but may affect the functional characteristics of the labelled antibody. In contrast, enzymatic signal amplification is a more practical and efficient strategy to improve sensitivity that should not affect antibody activity. Although enzymatic signal amplification still has a number of drawbacks, this approach is a promising strategy to analyse cell surface antigens.

Combinational biosynthesis and characterization of fusion proteins with tandem repeats of allophycocyanin holo-α subunits, and their application as bright fluorescent labels for immunofluorescence assay

Fusion protein of streptavidin and allophycocyanin holo-α subunit (ApcA) is fluorescent and is able to bind biotin. This fusion protein (SLA) can be used as fluorescent label in immunofluorescence assay. In this study, one or two repeats of ApcA were fused to the protein SLA, with the aim to improve its brightness. The fusion proteins SLA2 (two repeats of ApcA) and SLA3 (three repeats of ApcA), together with lyase (cpcS) and phycoerythrobilin synthesizing enzymes (Ho1 and PebS), were co-expressed in Escherichia coli. These fusion proteins were purified by affinity chromatography. While SLA2 and SLA3 shared similar absorbance spectra, fluorescence spectra and biotin-binding activities with SLA, their brightness were much higher than that of SLA. When used as fluorescent labels in immunofluorescence assay, SLA2 and SLA3 showed higher detection sensitivity than SLA. These results suggested that SLA2 and SLA3 were the preferable fluorescent labels in immunofluorescence assays.

Purification of R-phycoerythrin from Gracilaria lemaneiformis by centrifugal precipitation chromatography

Centrifugal precipitation chromatography (CpC) is a powerful chromatographic technique invented in the year 2000 but so far very little applied. The method combines dialysis, counter-current and salting out processes. The separation rotor consists of two identical spiral channels separated by a dialysis membrane (6-8 K MW cut-off) in which the upper channel is eluted with an ammonium sulfate gradient and the lower channel with water, and the mixtures are separated according to their solubility in ammonium sulfate as a chromatographic technique. In the present study, the method was successfully applied for separation and purification of R-phycoerythrin (R-PE), a protein widely used as a fluorescent probe, from the red alga Gracilaria lemaneiformis. The separation was performed with the elution of ammonium sulfate from 50% to 0% in 21.5 h at a flow rate of 0.5 ml/min, while the lower channel was eluted with water at a flow rate of 0.05 ml/min after sample charge, and the column was rotated at 200 rpm. After a single run, the absorbance ratio A₅₆₅/A₂₈₀ (a criterion for the purity of R-PE) was increased from 0.5 of the crude to 6.5. The purified R-PE exhibited a typical "three peaks" spectrum with absorbance maximum at 497, 538 and 565 nm. The Native-PAGE showed one single protein band and 20 kDa (subunits α and β) and 30 kDa (subunit γ) can be observed in SDS-PAGE analysis which were consistent with the (αβ)₆γ subunit composition of R-PE. The results indicated that CpC is an efficient method to obtain protein with the high purity from a complex source.

R-Phycoerythrin-labeled Mannheimia haemolytica for the simultaneous measurement of phagocytosis and intracellular reactive oxygen species production in bovine blood and bronchoalveolar lavage cells

The present study aimed to validate the use of R-phycoerythrin (R-PE)-labeled Mannheimia haemolytica to simultaneously stimulate phagocytosis and intracellular production of reactive oxygen species (ROS) by blood phagocytes in bronchoalveolar lavage (BAL) fluid. Initially, R-PE-labeled M. haemolytica was inactivated using a water bath at 60 °C for 60 min. Afterwards, R-PE labelling of bacteria was confirmed by flow cytometry. The geometric mean fluorescence intensity of R-PE-labeled bacteria (FL2 detector, 585 ± 42 nm) was analyzed by flow cytometry and was 41.5-fold higher than the respective unlabeled controls, confirming the success of bacterial conjugation to R-PE. Phagocytosis and intracellular production of ROS by blood neutrophils and monocytes, and by BAL CD14⁺ macrophages, in 12 healthy 6-month-old male calves were then performed using R-PE-labeled bacteria and 2',7'-dichlorofluorescein diacetate (DCFH-DA) as probes. Confocal microscopy was used to confirm phagocytosis of R-PE-labeled M. haemolytica by phagocytes and to exclude erroneous measurements of bacteria adhering to the leukocyte membrane. The present study showed that there is no difference in the ROS production without stimulus and in the presence of M. haemolytica by peripheral blood neutrophils and monocytes, in contrast to the increased ROS production by local alveolar macrophages upon stimulation by M. haemolytica. This emphasizes the importance of alveolar macrophages in the maintenance of homeostasis and health of the respiratory system, which can be supported during the inflammatory process by the rapid recruitment of neutrophils with high microbicidal and phagocytic capacity. The method described here provides an easy and feasible tool to measure phagocytosis and intracellular ROS production by phagocytes, especially when commonly used probes for intracellular ROS production were used, such as DCFH-DA and dihydrorhodamine 123.

Physico-chemical factors affecting the in vitro stability of phycobiliproteins from Phormidium rubidum A09DM

The functionality and stability of phycobiliproteins (PBPs) phycoerythrin (PE), phycocyanin (PC) and allophycocyanin (APC) were investigated under various temperatures, pHs and oxidative stressors. All PBPs were thermostable up to 4-40°C; however, their concentration decreased rapidly at 60-80°C. The maximum stability of all PBPs was in the pH range 6.0-7.0. Decrease in PBPs content was found under high acidic (pH 2-4) and alkaline conditions (pH 8-12). The oxidizing agent (0.1-0.6%) showed the least effect on the stability of PBPs; however, 0.8-1.0% H2O2 caused significant loss of PBPs. Contrary to PE, PC and APC was more susceptible to an oxidizing agent. The chromophore associated with α- and β-subunit of PBPs and thus, their functionality (fluorescence) was severely affected under high temperature (60-80°C), and oxidizing agent, as well as low (2-4) and high (8-12) pH. Contrary to PC and APC, functionality of PE was surprisingly maintained even at pHs 6-12 and under oxidative stress.

One-step purification of R-phycoerythrin from the red edible seaweed Grateloupia turuturu

A one-step chromatographic method for the purification of R-phycoerythrin (R-PE) of Grateloupia turuturu Yamada is described. Native R-PE was obtained with a purity index of 2.89 and a recovery yield of 27% using DEAE-Sepharose Fast Flow chromatography with a three-step increase in ionic strength. The analysis by SDS electrophoresis showed a broad band between 18 and 21kDa in size corresponding to subunits α and β and a low intensity band of 29kDa corresponding to the γ subunit. Two forms of R-PE were identified by gel filtration chromatography: a native form with a molecular weight of 260±5kDa and a dissociated form with a molecular weight of 60±2kDa. The native form presented the characteristic absorption spectrum of R-PE with three absorbance maxima at 498, 540 and 565nm, whereas the dissociated form presented only the 498 and 540nm peaks. Moreover, the two forms displayed two different fluorescence maxima.

Isolation, purification and properties of an R-Phycocyanin from the phycobilisomes of a marine red macroalga Polysiphonia urceolata

Phycobilisomes were prepared from a marine red macroalga Polysiphonia urceolata (P. urceolata) by sucrose step-gradient ultracentrifugation. From the prepared phycobilisomes, an R-phycocyanin was isolated by gel filtration on Sephadex G-150 and then purified by ion exchange chromatography on DEAE-Sepharose Fast Flow and native polyacrylamide gel electrophoresis (PAGE) performed in neutral buffer systems. The purified R-phycocyanins showed not only a homogeneous trimer of 136 kDa in gel filtration and a single band in native PAGE, but also exhibited one band at about pH 5.7 in native isoelectric focusing (IEF). By a gradient SDS-PAGE the purified R-phycocyanin was determined to contain one α subunit of 17.5 kDa (α^17.5) and two β subunits of 21.3 kDa and 22.6 kDa (β^21.3 and β^22.6). The analysis from denaturing isoelectric focusing and two-dimension PAGE demonstrated that α^17.5, β^21.3 and β^22.6 had their pIs of 6.4, 5.3 and 5.4, respectively. Furthermore, mass spectroscopy analysis of β^21.3 and β^22.6 by MALDI-TOF mass spectrometry demonstrated the two β subunits had differences in peptide mass fingerprinting. These results revealed that the prepared R-phycocyanins were composed of one α and two β subunits. and , which have a structural foundation to show their pIs too close for them to be definitely resolved by native IEF, are postulated to be the most possible trimeric forms of the R-phycocyanins prepared from the phycobilisomes of P. urceolata.

Recent developments in production and biotechnological applications of C-phycocyanin

An extensive range of pigments including phycobiliproteins are present in algae. C-phycocyanin (C-PC), a phycobiliprotein, is one of the key pigments of Spirulina, a microalgae used in many countries as a dietary supplement. Algal pigments have massive commercial value as natural colorants in nutraceutical, cosmetics, and pharmaceutical industries, besides their health benefits. At present, increasing awareness of harmful effects of synthetic compounds and inclination of community towards the usage of natural products have led to the exploitation of microalgae as a source of natural pigments/colors. This review describes recent findings about the sources and production of C-PC, with emphasis on specific techniques for extraction and purification, along with potential industrial applications in diagnostics, foods, cosmetics, and pharmaceutical industries.

Au nanostructures by colloidal lithography: from quenching to extensive fluorescence enhancement

Enhanced local electric fields are created by nanoparticles when pumped at wavelengths corresponding to Localised Surface Plasmon Resonance (LSPR) modes, leading to Metal Induced Fluorescence Enhancement (MIFE). This paper describes the fluorescent enhancement due to reproducible and tuneable Au nanostructures on glass substrates fabricated over large areas by colloidal lithography. Interparticle separation, particle resonance, and the fluorescent dye properties (quantum yield and emission/excitation wavelengths) are all important factors influencing the fluorescent enhancement. A maximum fluorescence enhancement of 69 times from near infra-red (NIR) dye Alexa Fluor® 790 was observed.

Fluorochromes: properties and characteristics

Immunofluorescence microscopy provides a sensitive means by which antigens can be localized within tissues or individual cells. For the most effective use of this technique the researcher can draw upon basic information on factors that affect the brightness of the fluorescence image, and how well that image can be distinguished from background fluorescence or interfering fluorescence signals. A wide variety of fluorochromes are available, with emitting wavelengths that range from the blue-violet end of the visible spectrum to the infrared. Individual fluorochromes are characterized by their extinction coefficients, quantum yields, susceptibility to photobleaching, the wavelengths at which they maximally absorb excitatory and emit fluorescent light, and how far apart those wavelength maxima are separated. Additional choices for fluorescent labeling of antibodies are provided by the availability of fluorescent quantum dots. Informed choices of fluorochromes can obviate many problems, particularly with regard to situations in which two or more antigens are to be localized simultaneously within a specimen.

Innovative natural functional ingredients from microalgae

Nowadays, a wide variety of compounds such as polyphenols, polyunsaturated fatty acids (PUFA), or phytosterols obtained, for example, from wine, fish byproducts, or plants are employed to prepare new functional foods. However, unexplored natural sources of bioactive ingredients are gaining much attention since they can lead to the discovery of new compounds or bioactivities. Microalgae have been proposed as an interesting, almost unlimited, natural source in the search for novel natural functional ingredients, and several works have shown the possibility to find bioactive compounds in these organisms. Some advantages can be associated with the study of microalgae such as their huge diversity, the possibility of being used as natural reactors at controlled conditions, and their ability to produce active secondary metabolites to defend themselves from adverse or extreme conditions. In this contribution, an exhaustive revision is presented involving the research for innovative functional food ingredients from microalgae. The most interesting results in this promising field are discussed including new species composition and bioactivity and new processing and extraction methods. Moreover, the future research trends are critically commented.

Isolation, purification and characteristics of R-phycoerythrin from a marine macroalga Heterosiphonia japonica

R-phycoerythrin is one of the three phycobiliproteins which are extensively employed as fluorescent probes, and it is prepared from red macroalgae. Phycobiliproteins in the marine red macroalga Heterosiphonia japonica were extracted in 50 mM phosphate buffer (pH 7.0) and precipitated by salting-out. The R-phycoerythrin was isolated by gel filtration with Sepharose CL-4B and Sephadex G-200. Then it was purified by ion exchange chromatography on DEAE Sepharose Fast Flow which was developed by linear ionic strength gradients. The purified R-phycoerythrin gave a ratio of A(565) to A(280) of 4.89. It showed a single band and a pI of 4.8 on the examination by polyacrylamide gel electrophoresis (PAGE) and isoelectric focusing. The polypeptide analysis of the purified R-phycoerythrin by SDS-PAGE demonstrated that it contains four chromophore-carrying subunits and no colorless polypeptide and has two hexameric aggregates. The preparative procedures of the R-phycoerythrin purification established based on the experiments exhibit advantages and can offer a reference for R-phycoerythrin preparation from other marine red macroalga.

Recent Advances in Fluorescence Cross-correlation Spectroscopy

Fluorescence cross-correlation spectroscopy (FCCS) is a method that measures the temporal fluorescence fluctuations coming from two differently labeled molecules diffusing through a small sample volume. Cross-correlation analysis of the fluorescence signals from separate detection channels extracts information of the dynamics of the dual-labeled molecules. FCCS has become an essential tool for the characterization of diffusion coefficients, binding constants, kinetic rates of binding, and determining molecular interactions in solutions and cells. By cross-correlating between two focal spots, flow properties could also be measured. Recent developments in FCCS have been targeted at using different experimental schemes to improve on the sensitivity and address their limitations such as cross-talk and alignment issues. This review presents an overview of the different excitation and detection methodologies used in FCCS and their biological applications. This is followed by a description of the fluorescent probes currently available for the different methods. This will introduce biological readers to FCCS and its related techniques and provide a starting point to selecting which experimental scheme is suitable for their type of biological study.

A Hexagonal Prismatic Porphyrin Array: Synthesis, STM Detection, and Efficient Energy Hopping in Near-Infrared Region

A belt-shaped hexagonal cyclic porphyrin array 2 that comprises of six meso-meso, beta-beta, beta-beta triply linked diporphyrins 3 bridged by 1,3-phenylene spacers is prepared by oxidation from cyclic dodecameric array 1 consisting of six meso-meso directly linked diporphyrins 4 with DDQ and Sc(OTf)3. The absorption spectrum of 2 is similar to that of the constituent subunit 3 but shows a slight red-shift for the Q-bands in near-infrared (NIR) region, indicating the exciton coupling between the neighboring diporphyrin chromophores. Observed total exciton coupling energies in the absorption spectra were largely matched with the calculated values based on point-dipole exciton coupling approximation. It was found that the experimental exciton coupling strength (292 cm(-1)) of the Q-band in 2 is slightly larger than the calculated one (99 cm(-1)), indicating that the electronic communications are enhanced through 1,3-phenylene linkers in hexameric macromolecule. A rate of the excitation energy hopping (EEH) that occurs in 2 at the lowest excited singlet state in the near-infrared region has been determined to be (1.8 ps)(-1) on the basis of the pump-power dependent femtosecond transient absorption (TA) and the transient absorption anisotropy (TAA) decay measurements. The 2 times faster EEH rate of 2 than that of 1 (4.0 ps)(-1) mainly comes from involving through-bond energy transfer among diporphyrin subunits via 1,3-phenylene bridges as well as Förster-type through-space EEH processes. STM measurement of 2 in the Cu(100) surface revealed that it takes several discrete conformations with respect to the relative orientation of neighboring diporphyrins. Collectively, an effective EEH in the NIR region is realized in 2 due largely to the intensified oscillator strength in the S(1) state (Q-band) and the close proximity held by 1,3-phenylene spacers.

Upconversion fluorescence resonance energy transfer in a homogeneous immunoassay for estradiol

We recently described a novel homogeneous assay principle based on upconversion fluorescence resonance energy transfer (UC-FRET), where an upconverting phosphor (UCP) is utilized as a donor. The UC-FRET has now been applied to a competitive homogeneous immunoassay for 17beta-estradiol (E2) in serum, using a small-molecular dye as an acceptor. The assay was constructed by employing an UCP coated with an E2-specific recombinant antibody Fab fragment as a donor and an E2-conjugated small-molecular dye, Oyster-556, as an acceptor. Standard curves for the assay were produced both in buffer and in male serum. Sensitized acceptor emission was measured at 600 nm under continuous laser diode excitation at 980 nm. In buffer, the IC50 value of the assay was 1 nM and in serum 3 nM. The lower limits of detection (mean of zero calibrators, 3 SD) were 0.4 and 0.9 nM, respectively. The measurable concentration range extended up to 3 nM in buffer and 9 nM in serum. Equilibrium in the assay was reached in 30 min. The novel principle of UC-FRET has unique advantages compared to present homogeneous luminescence-based methods and can enable an attractive assay system platform for clinical diagnostics and for high-throughput screening approaches.

Homogeneous assay technology based on upconverting phosphors

Upconversion photoluminescence can eliminate problems associated with autofluorescence and scattered excitation light in homogeneous luminescence-based assays without need for temporal resolution. We have demonstrated a luminescence resonance energy-transfer-based assay utilizing inorganic upconverting (UPC) lanthanide phosphor as a donor and fluorescent protein as an acceptor. UPC phosphors are excited at near-infrared and they have narrow-banded anti-Stokes emission at visible wavelengths enabling measurement of the proximity-dependent sensitized emission with minimal background. The acceptor alone does not generate any direct emission at shorter wavelengths under near-infrared excitation. A competitive model assay for biotin was constructed using streptavidin-conjugated Er3+,Yb3+-doped UPC phosphor as a donor and biotinylated phycobiliprotein as an acceptor. UPC phosphor was excited at near-infrared (980 nm) and sensitized acceptor emission was measured at red wavelength (600 nm) by using a microtitration plate fluorometer equipped with an infrared laser diode and suitable excitation and emission filters. Lower limit of detection was in the subnanomolar concentration range. Compared to time-resolved fluorometry, the developed assay technology enabled simplified instrumentation. Excitation at near-infrared and emission at red wavelengths render the technology also suitable to analysis of strongly colored and fluorescent samples, which are often of concern in clinical immunoassays and in high-throughput screening.

Homogeneous Silver-Coated Nanoparticle Substrates for Enhanced Fluorescence Detection

A simple method has been developed for the deposition of uniform silver-coated nanoparticles on glass substrates, with a homogeneous distribution shown by scanning electron microscopy (SEM). UV-visible spectroscopy and energy-dispersive X-ray analysis (EDX) have been used to characterize both the optical density and elemental content of the deposited nanoparticles. The fluorescence enhancement was investigated using a monolayer of FITC-conjugated human serum albumin (FITC-HSA) and tested using laser scanning microscopy at 488 nm excitation wavelength. The enhancement factor was calculated from individual spectra recorded with a Fluorolog-Tau-3 spectrofluorometer. We identified the nanoparticle growth regime which led to fluorescence enhancement. Such enhancement is detectable when Au core-Ag shell nanoparticles increased their size to 47 nm, in agreement with theoretical estimates. The origin of this enhancement for appropriate size nanoparticles is attributed to the effect of an increased excitation rate from the local field enhanced by the interaction of incident light with the nanoparticles and/or higher quantum yield from an increase of the intrinsic decay rate of the fluorophore. We thus demonstrated that the Au core-Ag shell nanostructures on glass surfaces are promising substrates for fluorescence enhancement with outstanding macroscopic homogeneity. This important feature will pave the way for the application of our substrates in biotechnology and life sciences such as imaging and sensing of biomolecules in proteomics.

Optimization and validation of a multiplexed luminex assay to quantify antibodies to neutralizing epitopes on human papillomaviruses 6, 11, 16, and 18

A human papillomavirus (HPV) multiplexed competitive Luminex immunoassay first described by Opalka et al. (D. Opalka, C. E. Lachman, S. A. MacMullen, K. U. Jansen, J. F. Smith, N. Chirmule, and M. T. Esser, Clin. Diagn. Lab. Immunol. 10:108--15, 2003) was optimized and validated for use in epidemiology studies and vaccine clinical trials. Optimization increased both the analytical sensitivity and the clinical specificity of the assay to more effectively discriminate the low-titer antibody response of HPV-infected persons from noninfected individuals. The characteristics of the assay that were optimized included monoclonal antibody (MAb) specificity, scaling up the conjugation of virus-like particles (VLPs) to microspheres, VLP concentration, MAb concentration, sample matrix, sample dilution, incubation time, heat inactivation of sample sera, and detergent effects on assay buffer. The assay was automated by use of a TECAN Genesis Workstation, thus improving assay throughput, reproducibility, and operator safety. Following optimization, the assay was validated using several distinct serum panels from individuals determined to be at low and high risk for HPV infection. The validated assay was then used to determine the clinical serostatus cutoff. This high-throughput assay has proven useful for performing epidemiology studies and evaluating the efficacy of prophylactic HPV vaccines.

Surface-enhanced fluorescence of fluorescein-labeled oligonucleotides capped on silver nanoparticles

Tiopronin monolayer-protected silver nanoparticles with different core sizes (average diameter = 2, 5, 20 nm) were prepared by using different mole ratios of silver nitrate/tiopronin. Ligands on the silver particles were partially displaced by fluorescein-labeled thiolate single-stranded oligonucleotides or their complementary unlabeled oligonucleotides through ligand exchange. The fluorophores on silver particles showed a surface-enhanced fluorescence (SEF) dependent on the size of metallic cores. The particles could be coupled through hybridizations of oligonucleotides bound on the particles. The coupled particles were aggregated due to multiple displacements of oligonucleotides on each particle, resulting in stronger SEF. The dye-labeled oligonucleotides were assembled on the silver islands on the solid substrate, and the complementary oligonucleotide-displaced particles were coupled via oligonucleotide hybridization. The couplings between particles and islands resulted in an obvious fluorescence enhancement.

Analysis of cyanobacterial pigments and proteins by electrophoretic and chromatographic methods

Cyanobacteria are a diverse and ubiquitous group of prokaryotes with several unifying features. Amongst these is the macromolecular structure known as the phycobilisome, which is composed of water-soluble phycobiliproteins covalently bound by linker peptides or proteins in a configuration designed to optimize energy transfer to the photosynthetic reaction center of the organism. Phycobiliproteins are highly fluorescent by virtue of their covalently bound, linear tetrapyrrole chromophores known as bilins. Analysis of these prosthetic pigments, along with other non-water soluble pigments, such as the chlorophylls and carotenoids, can provide insight into microbial diversity. The effects of environmental growth conditions and stresses can also be probed by measuring pigment and protein concentrations. This review will focus, therefore, on applications of various chromatographic and electrophoretic methods for the analysis of cyanobacterial pigment and protein constituents. Although the greatest emphasis will be placed on the measurement of bilins and phycobiliproteins, this review will also consider other pigments and proteins important to cyanobacterial growth and survival, such as chlorophyll a, carotenoids, ectoenzymes, linker and membrane proteins, and extracellular proteins.

Radiative decay engineering 4. Experimental studies of surface plasmon-coupled directional emission

Fluorescence is typically isotropic in space and collected with low efficiency. In this paper we describe surface plasmon-coupled emission (SPCE), which displays unique optical properties and can be collected with an efficiency near 50%. SPCE occurs for fluorophores within about 200 nm of a thin metallic film, in our case a 50-nm-thick silver film on a glass substrate. We show that fluorophore proximity to this film converts the normally isotropic emission into highly directional emission through the glass substrate at a well-defined angle from the normal axis. Depending on the thickness of the polyvinyl alcohol (PVA) film on the silver, the coupling efficiency of sulforhodamine 101 in PVA ranged from 30 to 49%. Directional SPCE was observed whether the fluorophore was excited directly or by the evanescent field due to the surface plasmon resonance. The emission is always polarized perpendicular to the plane of incidence, irrespective of the polarization of the incident light. The lifetimes are not substantially changed, indicating a mechanism somewhat different from that observed previously for the effects of silver particles on fluorophores. Remarkably, the directional emission shows intrinsic spectral resolution because the coupling angles depend on wavelength. The distances over which SPCE occurs, 10 to 200 nm, are useful because a large number of fluorophores can be localized within this volume. The emission of more distant fluorophores does not couple into the glass, allowing background suppression from biological samples. SPCE can be expected to become rapidly useful in a variety of analytical and medical sensing applications.

Radiative decay engineering 3. Surface plasmon-coupled directional emission

A new method of fluorescence detection that promises to increase sensitivity by 20- to 1000-fold is described. This method will also decrease the contribution of sample autofluorescence to the detected signal. The method depends on the coupling of excited fluorophores with the surface plasmon resonance present in thin metal films, typically silver and gold. The phenomenon of surface plasmon-coupled emission (SPCE) occurs for fluorophores 20-250 nm from the metal surface, allowing detection of fluorophores over substantial distances beyond the metal-sample interface. SPCE depends on interactions of the excited fluorophore with the metal surface. This interaction is independent of the mode of excitation; that is, it does not require evanescent wave or surface-plasmon excitation. In a sense, SPCE is the inverse process of the surface plasmon resonance absorption of thin metal films. Importantly, SPCE occurs over a narrow angular distribution, converting normally isotropic emission into easily collected directional emission. Up to 50% of the emission from unoriented samples can be collected, much larger than typical fluorescence collection efficiencies near 1% or less. SPCE is due only to fluorophores near the metal surface and may be regarded as emission from the induced surface plasmons. Autofluorescence from more distal parts of the sample is decreased due to decreased coupling. SPCE is highly polarized and autofluorescence can be further decreased by collecting only the polarized component or only the light propagating with the appropriate angle. Examples showing how simple optical configurations can be used in diagnostics, sensing, or biotechnology applications are presented. Surface plasmon-coupled emission is likely to find widespread applications throughout the biosciences.

Directional surface plasmon-coupled emission: A new method for high sensitivity detection

Fluorescence emission is nearly isotropic in space. With typical optical components the collection efficiency is 1% or less. In this preliminary report, we describe a novel approach to transforming the normally isotropic emission into directional emission with a collection efficiency near 50%. This can be accomplished for fluorophores located near a semi-transparent silver film on a glass substrate. The emission couples with the surface plasmon resonance on the silver surface and enters the transparent substrate at a sharply defined angle, the surface plasmon angle for the emission wavelength. We estimate that 40-70% of the total emission enters the substrate at the plasmon angle and can thus be directed towards a detector. Background emission from fluorophores distant from the silver does not couple with the plasmon and is not detected. Different emission wavelengths couple at different angles allowing spectral discrimination without additional optics. Surface plasmon-coupled emission represents a new technology which can be used for high detection efficiency with microfluidic and/or surface-bound assay formats.

Evaluation of Tolypothrix germplasm for phycobiliprotein content

Twenty Tolypothrix strains, including 15 strains of T. tenuis, three strains of T. ceylonica and one strain each of T. nodosa and T. bouteillei, were evaluated for their phycobiliprotein content and composition. Significant differences among the Tolypothrix strains were found at both inter- and intra-specific levels in the production of phycobiliprotein constituents--phycocyanin (PC), allophycocyanin (APC) and phycoerythrin (PE). Four specific parameters, viz. PC or PE content, total phycobiliprotein and total protein content, and percentage of phycobiliproteins, in a mixture of total proteins were used to select four T. tenuis and one T. ceylonica strain as useful for phycobiliproteins production.