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Rapid diagnostics are critical infectious disease tools that are designed to detect a known biomarker using antibodies specific to that biomarker. However, a way to detect unknown disease variants has not yet been achieved in a paper test format. We describe here a route to make an adaptable paper immunoassay that can detect an unknown biomarker, demonstrating it on SARS-CoV-2 variants. The immunoassay repurposes cross reactive antibodies raised against the alpha variant. Gold nanoparticles of two different colors conjugated to two different antibodies create a colorimetric signal, and machine learning of the resulting colorimetric pattern is used to train the assay to discriminate between variants of alpha and Omicron BA.5. By using principal component analysis, the colorimetric test patterns can pick up and discriminate an unknown variant that it has not encountered before, Omicron BA.1. The test has an accuracy of 100% and a potential calculated discriminatory power of 900. We show that it can be used adaptively and that it can be used to pick up emerging variants without the need to raise new antibodies.

The unique properties of plasmonic nanoparticles and nanostructures have enabled a broad range of applications in a diverse set of fields, ranging from biological sensing, cancer therapy, to catalysis. They have been some of the most studied nanomaterials due in part to their chemical stability and biocompatibility as well as supporting theoretical efforts. The synthesis and fabrication of plasmonic nanoparticles and nanostructures have now reached high precision and sophistication. We review here their fundamental optical properties, discuss their tailoring for biological environments, and then detail examples on how they have been used to innovate in the biological and biomedical fields., (© 2023. The Author(s), under exclusive license to Springer Nature Switzerland AG.)

Seafood contamination with Vibrio bacteria is a problem for aquaculture, especially with oysters, which are often consumed raw. Current methods for diagnosing bacterial pathogens in seafood involve lab-based assays such as polymerase chain reaction or culturing, which are time consuming and must occur in a centralized location. Detection of Vibrio in a point-of-care assay would be a significant tool for food safety control measures. We report here a paper immunoassay that can detect the presence of Vibrio parahaemolyticus (Vp) in buffer and oyster hemolymph. The test uses gold nanoparticles conjugated to polyclonal anti- Vibrio antibodies in a paper-based sandwich immunoassay. A sample is added to the strip and wicked through by capillary action. If Vp is present, it results in a visible color at the test area that can be read out by eyes or a standard mobile phone camera. The assay has a limit of detection of 6.05 × 10 5 cfu/mL and a cost estimate of $5 per test. Receiver operating characteristic curves with validated environmental samples showed a test sensitivity of 0.96 and a specificity of 1.00. Because the assay is inexpensive and can be used on Vp directly without the requirement for culturing, or sophisticated equipment, it has the potential to be used in fieldable settings., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

Background: Rapid antigen assays have been attractive for decentralized, point of care diagnostics because of their low cost, robustness, and ease of use. The development of a diagnostic assay for a newly emerging infectious disease needs to take into account the progression of a disease, whether there is human to human transmission, and patient biomarker levels with time, and these all impact the choice of antigen targets and affinity agents., Scope of Review: The factors involved in the biophysical design of rapid antigen immunoassays are discussed, focusing on antigen selection and designing for cross-reactivity. State of the art in the biophysical characterization of protein-ligand or antigen-antibody interactions, the different types of affinity agents used in immunoassays, and biochemical conjugation strategies are described., Major Conclusions: Antigen choice is a critical factor in immunoassay diagnostic development, and should account for the properties of the virion, virus, and disease progression. Biophysical and biochemical aspects of immunoassays are critical for performance., General Significance: This review can serve as an instructive guide to aid in diagnostic development for future emerging diseases., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Global public health infrastructure is unprepared for emerging pathogen epidemics, in part because diagnostic tests are not developed in advance. The recent Zika, Ebola, and SARS-CoV-2 virus epidemics are cases in point. We demonstrate here that multicolored gold nanoparticles, when coupled to cross-reactive monoclonal antibody pairs generated from a single immunization regimen, can be used to create multiple diagnostics that specifically detect and distinguish related viruses. The multiplex approach for specific detection centers on immunochromatography with pairs of antibody-conjugated red and blue gold nanoparticles, coupled with clustering algorithms to detect and distinguish related pathogens. Cross-reactive antibodies were used to develop rapid tests for i) Dengue virus serotypes 1-4, ii) Zika virus, iii) Ebola and Marburg viruses, and iv) SARS-CoV and SARS-CoV-2 viruses. Multiplexed rapid antigen tests based on multicolored nanoparticles and cross-reactive antibodies and can be developed prospectively at low cost to improve preparedness for epidemic outbreaks., Competing Interests: The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Lee Gehrke reports financial support was provided by National Institutes of Health (R33AI100190 and AI151807). Helena de Puig reports financial support was provided by Broshy Foundation. Helena de Puig reports financial support was provided by Tata Trusts. Lee Gehrke reports equipment, drugs, or supplies was provided by US Food and Drug Administration. Lee Gehrke reports a relationship with IDx20 that includes: consulting or advisory and equity or stocks. Irene Bosch reports a relationship with IDx20 that includes: board membership, employment, and equity or stocks. Nol Salcedo reports a relationship with IDx20 that includes: employment. Helena de Puig reports a relationship with IDx20 that includes: consulting or advisory. James Collins reports a relationship with Sherlock Biosciences that includes: board membership, consulting or advisory, and equity or stocks. Lee Gehrke has patent #9488613 issued to Massachusetts Institute of Technology. Irene Bosch, Kimberly Hamad-Schifferli, Helena de Puig has patent #9488613 issued to Massachusetts Institute of Technology. Lee Gehrke has patent #10551381 with royalties paid to Massachusetts Institute of Technology. Irene Bosch, Helena de Puig, Kimberly Hamad-Schifferli has patent #10551381 with royalties paid to Massachusetts Institute of Technology., (© 2022 The Authors.)

The effect of preformed protein coronas on immunoassays for Dengue nonstructural protein 1 (NS1) immunoassays was investigated. The composition of the protein corona that forms around nanoparticle-antibody conjugates in human serum was characterized, and selected proteins from the corona were used for preformed coronas (human serum albumin and apolipoprotein A1). Coronas were formed and characterized by dynamic light scattering (DLS), and the nanoparticle-conjugate was probed by optical absorption spectroscopy. Immunoassays were run, and performance was quantified by analyzing the strip intensity as a function of NS1 concentration. The preformed coronas influenced the limit of detection (LOD) of the assay and the affinity for the NS1 target ( K D ). The resulting K D and LODs for the NP-Ab-ApoA1 immunoprobes were 0.83 nM and 1.24 nM, respectively. For the NP-Ab -HSA coronas, the test line intensity was lower by 33% at a given NS1 concentration than for the NP-Ab immunoprobes, and K D was 0.14 nM, a slightly higher affinity. Due to the relatively large error of the negative control, a meaningful LOD for the NP-Ab with HSA coronas could not be determined.

Biosensors have been used for a remarkable array of applications, including infectious diseases, environmental monitoring, cancer diagnosis, food safety, and numerous others. In particular, the global COVID-19 pandemic has exposed a need for rapid tests, so the type of biosensor that has gained considerable interest recently are immunoassays, which are used for rapid diagnostics. The performance of paper-based lateral flow and dipstick immunoassays is influenced by the physical properties of the nanoparticles (NPs), NP-antibody conjugates, and paper substrate. Many materials innovations have enhanced diagnostics by increasing sensitivity or enabling unique readouts. However, negative side effects can arise at the interface between the biological sample and biomolecules and the NP or paper substrate, such as non-specific adsorption and protein denaturation. In this Perspective, we discuss the immunoassay components and highlight chemistry and materials innovations that can improve sensitivity. We also explore the range of bio-interface issues that can present challenges for immunoassays.

The COVID-19 pandemic has led to an unprecedented global health challenge, creating sudden, massive demands for diagnostic testing, treatment, therapies, and vaccines. In particular, the development of diagnostic assays for SARS-CoV-2 has been pursued as they are needed for quarantine, disease surveillance, and patient treatment. One of the major lessons the pandemic highlighted was the need for fast, cheap, scalable and reliable diagnostic methods, such as paper-based assays. Furthermore, it has previously been suggested that paper-based tests may be more suitable for settings with lower resource availability and may help alleviate some supply chain challenges which arose during the COVID-19 pandemic. Therefore, we explore how such devices may fit in a comprehensive diagnostic strategy and how some of the challenges to the technology, e.g. low sensitivity, may be addressed. We discuss the properties of the SARS-CoV-2 virus itself, the COVID-19 disease pathway, and the immune response. We then describe the different diagnostic strategies that have been pursued, focusing on molecular strategies for viral genetic material, antigen tests, and serological assays, and innovations for improving the diagnostic sensitivity and capabilities. Finally, we discuss pressing issues for the future, and what needs to be addressed for the ongoing pandemic and future outbreaks.

COVID-19 first appeared in December of 2019 in Wuhan, China. Since then, it has become a global pandemic. A robust and scalable diagnostics strategy is crucial for containing and monitoring the pandemic. RT-PCR is a known, reliable method for COVID-19 diagnostics, which can differentiate between SARS-CoV-2 and other viruses. However, PCR is location-dependent, time-consuming, and relatively expensive. Thus, there is a need for a more flexible method, which may be produced in an off-the-shelf format and distributed more widely. Paper-based immunoassays can fulfill this function. Here, we present the first steps toward a paper-based test, which can differentiate between different spike proteins of various coronaviruses, SARS-CoV-1, SARS-CoV-2, and CoV-HKU1, with negligible cross-reactivity for HCoV-OC43 and HCoV-229E in a single assay, which takes less than 30 min. Furthermore, our test can distinguish between fractions of the same spike protein. This is done by an altered assay design with four test line locations where each antigen builds a unique, identifiable binding pattern. The effect of several factors, such as running media, immunoprobe concentration, and antigen interference, is considered. We find that running media has a significant effect on the final binding pattern where human saliva provides results while human serum leads to the lowest signal quality.

As new infectious disease outbreaks become more likely, it is important to be able to develop and deploy appropriate testing in time. Paper-based immunoassays are rapid, cheap, and easy to produce at scale and relatively user friendly but often suffer from low selectivity and sensitivity. Understanding the molecular mechanisms of paper immunoassays may help improve and hasten development and therefore production and market availability. Here, we study how the behavior of nanoparticle-antibody immunoprobes in paper dipstick immunoassays is impacted by synthesis strategy and surface chemistry architecture. We conjugate gold nanoparticles to polyclonal anti-immunoglobulin G (IgG) and anti-zika NS1 antibodies by electrostatic adsorption and N -hydroxysuccinimide (NHS) and hydrazide (Hz) chemistries. The immunoprobes were used in paper immunoassays and the effective affinity for the antigen was quantified from the test line intensities, as well as the distribution of the immunoprobes throughout the strips. The results show that nanoparticle colloidal stability, both post synthesis and during antigen binding, is a key factor and affects immunoassay results and performance, often through reduction or loss of signal.

We exploit the cross-reactivity of dengue (DENV) and Zika (ZIKV) virus polyclonal antibodies for nonstructural protein 1 (NS1) to construct a selective sensor that can detect yellow fever virus (YFV) NS1 in a manner similar to chemical olfaction. DENV and ZIKV antibodies were screened for their ability to bind to DENV, ZIKV, and YFV NS1 by enzyme linked immunosorbent assay (ELISA) and in pairs in paper immunoassays. A strategic arrangement of antibodies immobilized on paper and conjugated to different colored gold NPs was used to distinguish the three biomarkers. Machine learning of test area RGB values showed that with two spots, readout accuracies of 100% and 87% were obtained for both pure NS1 and DENV/YFV mixtures, respectively. Additional image preprocessing allowed differentiation between all four DENV serotypes with 92% accuracy. The technique was extended to hack a commercial DENV test to detect YFV and ZIKV by augmentation with DENV and ZIKV polyclonal antibodies.

The detection of foodborne pathogens is critical for disease control and infection prevention, especially in seafood consumed raw or undercooked. Paper-based diagnostic tools are promising for rapid fieldable detection and provide a readout by eye due to the use of gold nanoparticle immunoprobes. Here we study different strategies to overcome these challenges in a real biological matrix, oyster hemolymph, for the detection of the pathogenic bacteria Vibrio parahaemolyticus (Vp). Nanoparticle surface chemistry, nitrocellulose speed and blocking, running steps, and antibody concentrations on the NP and nitrocellulose were all studied. Their effect on paper immunoassay signal intensity was quantified to determine optimal conditions, which enabled the detection of Vp directly from hemolymph below pathogenic concentrations.

Historically, many industries such as manufacturing have undergone a trend away from centralized, large-scale production toward a more distributed form. Currently, this same trend is witnessed in biological manufacturing and bioprocessing, with the rise of biological foundries where one can synthesize, grow, isolate, and purify a broad range of biologics. The adoption of distributed practices for biological processing has significant implications for healthcare, diagnostics, and therapies. This essay discusses the many diverse factors that have facilitated this growth, ranging from the establishment of available biological components, or "parts," low-cost programmable hardware, and others. Currently existing examples of distributed biological foundries are also identified, separating the discussion into those that are accessible only by elite users and the more recent emerging foundries that are more accessible to the general population. Taking lessons from other fields, it is argued that this trend toward distributed biological manufacturing is inevitable, so adapting to this trend is important for the progress of creating new therapeutics, sensors, diagnostics, and reagents for biomedical applications., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Myxovirus protein A (MxA) is a biomarker that can be used to distinguish between viral and bacterial infections. While MxA lateral flow assays (LFAs) have been successfully used for viral vs. bacterial differential diagnosis for children, the clinically relevant level of MxA for adults has been reported to be 100 times lower, which is too low for traditional LFAs. We present results applying the use of surface enhanced Raman spectroscopy (SERS) to detect MxA. AuAg nanoshells (AuAg NSs) were used to enhance the Raman signal of mercaptobenzoic acid (4-MBA), enabling readout by SERS. The AuAg NSs were conjugated to antibodies for the biomarker of interest, resulting in a "nanotag", that could be used in a dipstick immunoassay for detection. We first optimized the nanotag parameters using anti-human IgG/human IgG as a model antibody/antigen system, and then demonstrated detection of MxA using anti-MxA antibodies. We show that SERS readout of immunoassays for MxA can quantify MxA levels at clinically relevant levels for adult viral infection.

Quantification of biology's central dogma (transcription and translation) is pursued by a variety of methods. Direct, immediate, and ongoing quantification of these events is difficult to achieve. Common practice is to use fluorescent or luminescent proteins to report indirectly on prior cellular events, such as turning on a gene in a genetic circuit. We present an alternative approach, PURExpress-ReAsH-Spinach In-vitro Analysis (PERSIA). PERSIA provides information on the production of RNA and protein during cell-free reactions by employing short RNA and peptide tags. Upon synthesis, these tags yield quantifiable fluorescent signal without interfering with other biochemical events. We demonstrate the applicability of PERSIA in measuring cell-free transcription, translation, and other enzymatic activity in a variety of applications: from sequence-structure-function studies, to genetic code engineering, to testing antiviral drug resistance.

The effect of matrix metalloproteinases (MMPs) on preformed protein coronas around spherical gold nanoparticles (AuNPs) was studied. Protein coronas of different compositions (human serum, human serum albumin, and collagen IV) were formed around AuNPs and characterized. The protease MMP-9 had different effects on the corona depending on the corona composition, resulting in different changes to the corona hydrodynamic diameter ( D H ). When incubated with PANC-1 cells, the corona showed evidence of both increases as well as decreases in D H . Varying the composition of the corona influenced the MMP-9 activity. Furthermore, the corona was influenced not only by the protease activity of the MMP-9 but also by its ability to exchange with proteins in the preformed corona. This exchange could also occur with proteins in the media. Thus, the net effect of the MMP-9 was a combination of the MMP-9 protease activity and also exchange. Time scales for the exchange varied depending on the nature that make up the protein corona (weakly vs strongly bound corona proteins). Mass spectrometry was used to probe the protein corona composition and supported the exchange and degradation model. Together, these results indicate that the mechanism of protease activity on AuNP coronas involves both rearrangement and exchange, followed by degradation.

Paper-based sensors and assays have been highly attractive for numerous biological applications, including rapid diagnostics and assays for disease detection, food safety, and clinical care. In particular, the paper immunoassay has helped drive many applications in global health due to its low cost and simplicity of operation. This review is aimed at examining the fundamentals of the technology, as well as different implementations of paper-based assays and discuss novel strategies for improving their sensitivity, performance, or enabling new capabilities. These innovations can be categorized into using unique nanoparticle materials and structures for detection via different techniques, novel biological species for recognizing biomarkers, or innovative device design and/or architecture.

We report a quantitative evaluation of the choice of reporters for multiplexed surface-enhanced Raman spectroscopy (SERS). An initial library consisted of 15 reporter molecules that included commonly used Raman dyes, thiolated reporters, and other small molecules. We used a correlation matrix to downselect Raman reporters from the library to choose five candidates: 1,2-bis(4-pyridyl)ethylene, 4-mercaptobenzoic acid, 3,5-dichlorobenzenthiol, pentachlorothiophenol, and 5,5'-dithiobis(2-nitrobenzoic acid). We evaluated the ability to distinguish the five SERS reporters in a dipstick immunoassay for the biomarker human IgG. Raman nanotags, or gold nanostars conjugated to the five reporters and anti-human IgG polyclonal antibodies were constructed. A linear discriminant analysis approach was used to evaluate the separation of the nanotag spectra in mixtures of fixed ratios., Competing Interests: The authors declare no competing financial interest.

The design and fabrication of reconfigurable, modular paperfluidics driven by a prefabricated reusable block library, asynchronous modular paperfluidic linear instrument-free (Ampli) block, are reported. The blocks are inspired by the plug-and-play modularity of electronic breadboards that lower prototyping barriers in circuit design. The resulting biochemical breadboard is a paperfluidic construction set that can be functionalized with chemical, biological, and electrical elements. Ampli blocks can form standard paperfluidic devices without any external instrumentation. Furthermore, their modular nature enhances fluidics in ways that fixed devices cannot. The blocks' ability to start, stop, modify, and reverse reaction flows, reagents, and rates in real time is demonstrated. These enhancements allow users to increase colorimetric signals, fine tune reaction times, and counter check multiplexed diagnostics for false positives or negatives. The modular construction demonstrates that field-ready, distributed fabrication of paper analytical systems can be standardized without requiring the "black box" of craft and technique inherent in paper-based systems. Ampli assembly and point-of-care redesign extends the usability of paper analytical systems and invites user-driven prototyping beyond the lab setting demonstrating "Design for Hack" in diagnostics., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The unique size and material dependent properties of nanoparticles have made them highly attractive for biological and medical applications. However, combining nanoparticles with biomolecules and biological environments has faced many challenges. These interface issues often involve protein denaturation, steric hindrance, and orientational issues for the biomolecule, which can impair function and decrease overall performance of the nanoparticle-biomolecule conjugate. Historically, our understanding of the physical and chemical properties of nanoparticle-biomolecule conjugates as appropriate tools and experimental techniques had to be determined. We discuss here selected examples investigating the fundamental physical properties of the interface between nanoparticles and DNA and proteins and protein coronas and how they have provided insight into the properties of the biomolecule when it is interfaced to a nanoparticle.

Lateral flow assays (LFAs) are highly attractive for point-of-care (POC) diagnostics for infectious disease, food safety, and many other medical uses. The unique optical, electronic, and chemical properties that arise from the nanostructured and material characteristics of nanoparticles provide an opportunity to increase LFA sensitivity and impart novel capabilities. However, interfacing to nanomaterials in complex biological environments is challenging and can result in undesirable side effects such as non-specific adsorption, protein denaturation, and steric hindrance. These issues are even more acute in LFAs where there are many different types of inorganic-biological interfaces, often of a complex nature. Therefore, the unique properties of nanomaterials for LFAs must be exploited in a way that addresses these interface challenges., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Zika and dengue are mosquito-borne diseases that present similar nonspecific symptoms but possess dramatically different outcomes. The first line of defense in epidemic outbreaks are rapid point-of-care diagnostics. Because many outbreaks occur in areas that are resource poor, assays that are easy to use, inexpensive, and require no power have become invaluable in patient treatment, quarantining, and surveillance. Paper-based sandwich immunoassays such as lateral flow assays (LFAs) are attractive as point-of-care solutions as they have the potential for wider deployability than lab-based assays such as PCR. However, their low sensitivity imposes limitations on their ability to detect low biomarker levels and early diagnosis. Here, we exploit the high sensitivity of surface-enhanced Raman spectroscopy (SERS) in a multiplexed assay that can distinguish between Zika and dengue nonstructural protein 1 (NS1) biomarkers. SERS-encoded gold nanostars were conjugated to specific antibodies for both diseases and used in a dipstick immunoassay, which exhibited 15-fold and 7-fold lower detection limits for Zika NS1 and dengue NS1, respectively. This platform combines the simplicity of a LFA with the high sensitivity of SERS and could not only improve Zika diagnosis but also detect diseases sooner after infection when biomarker levels are low.

Surface enhanced Raman spectroscopy (SERS) has been attractive for enhancing the sensitivity of lateral flow immunoassays (LFA). A format that has enabled specific detection of biomarkers is to use Raman reporter molecules linked to gold nanoparticles (NPs), which are conjugated to antibodies specific for the target of interest. Many factors such as the NP and Ab properties and the method of signal readout impact the sensitivity of a SERS based immunoassay. To understand how to optimize assay sensitivity, we studied SERS readouts of multiplexed sandwich immunoassays for the zika and dengue non-structural protein 1 (NS1) biomarkers as a test case. We investigated the effect of NP shape on the SERS enhancement of the reporter molecules 1,2-bis(4-pyridyl)ethylene (BPE) and 4-mercaptobenzoic acid (MBA). We also performed SERS imaging of test lines to map the spatial distribution of signal in test lines on the nitrocellulose. Finally, we used a modified least squares analysis to differentiate reporter contributions.

The recent Zika virus (ZIKV) outbreak demonstrates that cost-effective clinical diagnostics are urgently needed to detect and distinguish viral infections to improve patient care. Unlike dengue virus (DENV), ZIKV infections during pregnancy correlate with severe birth defects, including microcephaly and neurological disorders. Because ZIKV and DENV are related flaviviruses, their homologous proteins and nucleic acids can cause cross-reactions and false-positive results in molecular, antigenic, and serologic diagnostics. We report the characterization of monoclonal antibody pairs that have been translated into rapid immunochromatography tests to specifically detect the viral nonstructural 1 (NS1) protein antigen and distinguish the four DENV serotypes (DENV1-4) and ZIKV without cross-reaction. To complement visual test analysis and remove user subjectivity in reading test results, we used image processing and data analysis for data capture and test result quantification. Using a 30-μl serum sample, the sensitivity and specificity values of the DENV1-4 tests and the pan-DENV test, which detects all four dengue serotypes, ranged from 0.76 to 1.00. Sensitivity/specificity for the ZIKV rapid test was 0.81/0.86, respectively, using a 150-μl serum input. Serum ZIKV NS1 protein concentrations were about 10-fold lower than corresponding DENV NS1 concentrations in infected patients; moreover, ZIKV NS1 protein was not detected in polymerase chain reaction-positive patient urine samples. Our rapid immunochromatography approach and reagents have immediate application in differential clinical diagnosis of acute ZIKV and DENV cases, and the platform can be applied toward developing rapid antigen diagnostics for emerging viruses., (Copyright © 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

We investigated the effect of the protein corona on the function of nanoparticle (NP) antibody (Ab) conjugates in dipstick sandwich immunoassays. Ab specific for Zika virus nonstructural protein 1 (NS1) were conjugated to gold NPs, and another anti-NS1 Ab was immobilized onto the nitrocellulose membrane. Sandwich immunoassay formation was influenced by whether the strip was run in corona forming conditions, i.e., in human serum. Strips run in buffer or pure solutions of bovine serum albumin exhibited false positives, but those run in human serum did not. Serum pretreatment of the nitrocellulose also eliminated false positives. Corona formation around the NP-Ab in serum was faster than the immunoassay time scale. Langmuir binding analysis determined how the immobilized Ab affinity for the NP-Ab/NS1 was impacted by corona formation conditions, quantified as an effective dissociation constant, K D eff . Results show that corona formation mediates the specificity and sensitivity of the antibody-antigen interaction of Zika biomarkers in immunoassays, and plays a critical but beneficial role.

Point-of-care (POC) diagnostics such as lateral flow and dipstick immunoassays use gold nanoparticle (NP)-antibody conjugates for visual readout. We investigated the effects of NP conjugation, surface chemistries, and antibody immobilization methods on dipstick performance. We compared orientational, covalent conjugation, electrostatic adsorption, and a commercial conjugation kit for dipstick assays to detect dengue virus NS1 protein. Assay performance depended significantly on their conjugate properties. We also tested arrangements of multiple test lines within strips. Results show that orientational, covalent conjugation with PEG shield could improve NS1 detection. These approaches can be used to optimize immunochromatographic detection for a range of biomarkers.

Gold nanostars (NStars) are highly attractive for biological applications due to their surface chemistry, facile synthesis and optical properties. Here, we synthesize NStars in HEPES buffer at different HEPES/Au ratios, producing NStars of different sizes and shapes, and therefore varying optical properties. We measure the extinction coefficient of the synthesized NStars at their maximum surface plasmon resonances (SPR), which range from 5.7 × 10 8 to 26.8 × 10 8 M -1 cm -1 . Measured values correlate with those obtained from theoretical models of the NStars using the discrete dipole approximation (DDA), which we use to simulate the extinction spectra of the nanostars. Finally, because NStars are typically used in biological applications, we conjugate DNA and antibodies to the NStars and calculate the footprint of the bound biomolecules.

In this paper, we report on a method to probe the breakdown of the organophosphate (OP) simulants o,s-diethyl methyl phosphonothioate (OSDMP) and demeton S by the enzyme organophosphorous hydrolase (OPH) in a microfluidic device by surface enhanced Raman spectroscopy (SERS). SERS hotspots were formed on-demand inside the microfluidic device by laser-induced aggregation of injected Ag NPs suspensions. The Ag NP clusters, covering micron-sized areas, were formed within minutes using a conventional confocal Raman laser microscope. These Ag NP clusters were used to enhance the Raman spectra of the thiol products of OP breakdown in the microfluidic device: ethanethiol (EtSH) and (ethylsulfanyl) ethane-1-thiol (2-EET). When the OPH enzyme and its substrates OSDMP and demeton S were introduced, the thiolated breakdown products were generated, resulting in changes in the SERS spectra. With the ability to analyze reaction volumes as low as 20 nL, our approach demonstrates great potential for miniaturization of SERS analytical protocols.

Protein coronas have been the focus of a great deal of study recently due to their inevitable formation and their impact on the biological consequences of nanomaterials. Although the field is still far from completely and definitively understanding protein coronas, we now have a good understanding of their behavior and their key characteristics. Protein corona composition changes with the environment and time, and also the physical properties of the underlying nanoparticle. More importantly, the protein corona has significant biological impact. Because we have a basic understanding of coronas, we can now move forward to exploiting their unique properties. Here, we discuss some emerging ways in which the protein corona is explicitly utilized for different applications in biology and medicine.

Rapid point-of-care (POC) diagnostic devices are needed for field-forward screening of severe acute systemic febrile illnesses. Multiplexed rapid lateral flow diagnostics have the potential to distinguish among multiple pathogens, thereby facilitating diagnosis and improving patient care. Here, we present a platform for multiplexed pathogen detection using multi-colored silver nanoplates. This design requires no external excitation source and permits multiplexed analysis in a single channel, facilitating integration and manufacturing.

We probe how amphiphilic ligands (ALs) of four different types affect the formation of protein coronas on gold nanorods (NRs) and their impact on cellular response. NRs coated with cetyltrimethylammonium bromide were ligand exchanged with polyoxyethylene[10]cetyl ether, oligofectamine, and phosphatidylserine (PS). Protein coronas from equine serum (ES) were formed on these NR-ALs, and their colloidal stability, as well as cell uptake, proliferation, oxidative stress, and gene expression, were examined. We find that the protein corona that forms and its colloidal stability are affected by AL type and that the cellular response to these NR-AL-coronas (NR-AL-ES) is both ligand and corona dependent. We also find that the presence of common cell culture supplement penicillin/streptomycin can impact the colloidal stability and cellular response of NR-AL and NR-AL-ES, showing that the cell response is not necessarily inert to pen/strep when in the presence of nanoparticles. Although the protein corona is what the cells see, the underlying surface ligands evidently play an important role in shaping and defining the physical characteristics of the corona, which ultimately impacts the cellular response. Further, the results of this study suggest that the cellular behavior toward NR-AL is mediated by not only the type of AL and the protein corona it forms but also its resulting colloidal stability and interaction with cell culture supplements.

We investigate the activity of glucose oxidase (GOx) together with horseradish peroxidase (HRP) on carbon nanoparticles (CNPs). Because GOx activity relies on HRP, we probe how the arrangement of the enzymes on the CNPs affects enzymatic behavior. Colorimetric assays to probe activity found that the coupling strategy affects activity of the bienzyme-nanoparticle complex. GOx is more prone than HRP to denaturation on the CNP surface, where its activity is compromised, while HRP activity is enhanced when interfaced to the CNP. Thus, arrangements where HRP is directly on the surface of the CNP and GOx is not are more favorable for overall activity. Coverage also influenced activity of the bienzyme complex, but performing the conjugation in the presence of glucose did not improve GOx activity. These results show that the architecture of the assembly is an important factor in optimization of nanoparticle-protein interfaces., (Published by Elsevier Inc.)

We manipulate the passive release rates of DNA payloads on protein coronas formed around nanoparticles (NPs) by varying the corona composition. The coronas are prepared using a mixture of hard and soft corona proteins. We form coronas around gold nanorods (NRs), nanobones (NBs), and carbon nanotubes (CNTs) from human serum (HS) and find that tuning the amount of human serum albumin (HSA) in the NR-coronas (NR-HS-DNA) changes the payload release profile. The effect of buffer strength, HS concentration, and concentration of the cetyltrimethylammonium bromide (CTAB) passivating the NP surfaces on passive release is explored. We find that corona properties play an important role in passive release, and concentrations of CTAB, HS, and phosphate buffer used in corona formation can tune payload release profiles. These advances in understanding protein corona properties bring us closer toward developing a set of basic design rules that enable their manipulation and optimization for particular biological applications.

Blood clotting is a precise cascade engineered to form a clot with temporal and spatial control. Current control of blood clotting is achieved predominantly by anticoagulants and thus inherently one-sided. Here we use a pair of nanorods (NRs) to provide a two-way switch for the blood clotting cascade by utilizing their ability to selectively release species on their surface under two different laser excitations. We selectively trigger release of a thrombin binding aptamer from one nanorod, inhibiting blood clotting and resulting in increased clotting time. We then release the complementary DNA as an antidote from the other NR, reversing the effect of the aptamer and restoring blood clotting. Thus, the nanorod pair acts as an on/off switch. One challenge for nanobiotechnology is the bio-nano interface, where coronas of weakly adsorbed proteins can obscure biomolecular function. We exploit these adsorbed proteins to increase aptamer and antidote loading on the nanorods.

Self-assembled monolayers of Thrombin Binding Aptamers (TBA) were prepared on gold surfaces with typical surface densities of close-packed ssDNA (4×10(12) and 8×10(12)molecules/cm(2)). CONtact Angle MOlecular REcognition (CONAMORE) in captive bubble geometry was then assessed to scan the surface work triggered by TBAs when switching from the elongated to the G-quadruplex conformation upon binding with Na(+) or K(+) cations. We found Na(+) and K(+) could induce comparable linear to G-quadruplex strokes, and resulted in values for surface work of ~-70 pN nm/molecule (~18 kBT). The strokes change the in-plane van der Waals and weak electrostatic interactions and accumulate to result in macroscopic surface work. Micro- to macroscopic translation strongly depends on the nature of the cation and TBA surface density. In particular, the K(+) stimulus triggers a macroscopic surface work of -2.2±0.2 and -5.3±0.2 mN/m for low and high packed monolayers, respectively, while Na(+) triggers up to -6.7±1.0 mN/m in the highly packed monolayer, but creates negligible work for the low packed monolayer. These results show that CONAMORE can contribute important information for the development of devices based on DNA switches, and ultimately help address some of the open challenges for DNA-based nanomachinery., (Copyright © 2013 Elsevier Inc. All rights reserved.)

The ability to direct bimetallic nanoparticles to express desirable surface composition is a crucial step toward effective heterogeneous catalysis, sensing, and bionanotechnology applications. Here we report surface composition tuning of bimetallic Au-Pt electrocatalysts for carbon monoxide and methanol oxidation reactions. We establish a direct correlation between the surface composition of Au-Pt nanoparticles and their catalytic activities. We find that the intrinsic activities of Au-Pt nanoparticles with the same bulk composition of Au0.5Pt0.5 can be enhanced by orders of magnitude by simply controlling the surface composition. We attribute this enhancement to the weakened CO binding on Pt in discrete Pt or Pt-rich clusters surrounded by surface Au atoms. Our finding demonstrates the importance of surface composition control at the nanoscale in harnessing the true electrocatalytic potential of bimetallic nanoparticles and opens up strategies for the development of highly active bimetallic nanoparticles for electrochemical energy conversion.

We form coronas of serum proteins on gold nanorods (NRs) coated with cetyltrimethylammonium bromide (CTAB). These coronas can be exploited for their ability to hold small molecular therapeutics at a capacity much higher (~5-10×) than what covalent conjugation strategies can achieve. Coronas are loaded with DNA oligonucleotides and Doxorubicin, showing that they can hold species of either negative or positive charge. Payload capacity varies with assembly strategy, ionic strength, and loading concentration. Payload release can be achieved by increasing the temperature or by ultrafast laser excitation of the NRs at their longitudinal surface plasmon resonance. DNA leakage from the corona is minimal within the first 3 days of preparation, although Dox leakage was more significant. The coronas also stabilize the NRs in buffer and biological media. This study demonstrates the biological utility of the protein corona around nanomaterials, contrasting the common view of the corona as an undesirable biological response.

The stability of gold nanorods (NRs) coated with amphiphilic ligands (ALs) was investigated. NRs coated with cetyltrimethylammonium bromide (CTAB) were ligand exchanged with polyoxyethylene [10] cetyl ether (Brij56), Oligofectamine (OF), and phosphatidylserine (PS). An aggregation index based on the longitudinal surface plasmon resonance peak broadening was used to measure stability of the NR-ALs under different conditions including the number of washes, pH, ionic concentration, and temperature. The aggregation index was also used to measure the stability of the NR-ALs under ultrafast laser irradiation and in the presence of proteins commonly used in cell culture. Differences in NR-AL stability were found, which were due to differences in the physical and chemical properties of the ALs. Apart from the charge on the AL headgroup, we suggest the Gibbs free energy of passivation (ΔG(p)) and enthalpy of passivation (ΔH(p)) of the AL could potentially aid in the selection of amphiphiles that can effectively passivate NRs for stability and optimize their properties and desired biological impact.

The oxidation of AuCu nanoparticles was studied as a function of composition and temperature. Oxidation rates at 110 °C were higher for NPs with higher Cu content, showing that Au stabilized the Cu. Electrochemistry measurements show that AuCu could be a promising catalyst for lowering the over potential of CO(2) reduction.

The behavior of glucose oxidase (GOx) on gold nanoparticles (NPs) was investigated as a function of (1) NP surface chemistry, (2) stabilizing protein additives, and (3) protein microenvironment. GOx secondary structure and unfolding was probed by circular dichroism (CD) spectroscopy and fluorescence, and GOx enzymatic activity was measured by a colorimetric assay. We also examined the activity and structure of GOx after displacement from the NP surface. Generally, GOx behavior was negatively impacted by conjugation to the NP, and conjugation conditions could vary the influence of the NP. Surface chemistry and protein microenvironment could improve behavior, but addition of stabilizing proteins negatively influenced activity. After displacement from the NPs, GOx tended to remain unfolded, indicating that the interactions with the NP were irreversible.

A study is presented of the nanomechanical phenomena experienced by nanoparticle-conjugated biomolecules. A thermodynamic framework is developed to describe the binding of thrombin-binding aptamer (TBA) to thrombin when the TBA is conjugated to nanorods. Binding results in nanorod aggregation (viz. directed self-assembly), which is detectable by absorption spectroscopy. The analysis introduces the energy of aggregation, separating it into TBA-thrombin recognition and surface-work contributions. Consequently, it is demonstrated that self-assembly is driven by the interplay of surface work and thrombin-TBA recognition. It is shown that the work at the surface is about -10 kJ mol(-1) and results from the accumulation of in-plane molecular forces of pN magnitude and with a lifetime of <1 s, which arises from TBA nanoscale rearrangements fuelled by thrombin-directed nanorod aggregation. The obtained surface work can map aggregation regimes as a function of different nanoparticle surface conditions. Also, the thermodynamic treatment can be used to obtain quantitative information on surface effects impacting biomolecules on nanoparticle surfaces., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Gold nanorods (GNRs) stabilized with cetyltrimethylammonium bromide (CTAB) and GNR functionalized via a ligand exchange method with either thiolated polyethylene glycol (PEG(5000)) or mercaptohexadecanoic acid (MHDA) were investigated for their stability in biological media and subsequent toxicological effects to HaCaT cells. GNR-PEG and GNR-MHDA exhibited minimal effects on cell proliferation, whereas GNR-CTAB reduced cell proliferation significantly due to the inherent toxicity of the cationic surfactant to cells. Cell uptake studies indicated relatively low uptake for GNR-PEG and high uptake for GNR-MHDA. Reverse transcriptase polymerase chain reaction (RT-PCR) revealed that GNR-PEG induced less significant and unique changes in the transcription levels of 84 genes related to stress and toxicity compared to GNR-MHDA. The results demonstrate that, although cell proliferation was not affected by both particles, there is a significant difference in gene expression in GNR-MHDA exposed cells, suggesting long-term implications for chronic exposure.

We report the first example of microcantilever beams that are reversibly driven by protein thin film machines fueled by cycling the salt concentration of the surrounding solution. We also show that upon the same salinity stimulus the drive can be completely reversed in its direction by introducing a surface coating ligand. Experimental results are throughout discussed within a general yet simple thermodynamic model.