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In this paper, we use an ion-exchange membrane disk to develop miniaturized concentration device, which employs gold nanoparticle (GNP) colorimetric assay to determine human serum albumin content in artificial urine samples. When an external field is applied across cation exchange substrate, the ion depletion appears on the anodic side when the ions are enriched on the cathodic side to fulfill mass conservation and electrical neutrality constrains. In particular when the ion exchange substrates are of round shape, the field lines passing through the membrane disk are focused at the exit pole to further enhance concentration polarization to result in a superconcentraiton spot. GNP colorimetric assays to determine albumin are carried out using the miniaturized concentration chip containing a Nafion ® cation-exchange membrane disk. Under alkaline condition when GNP solution is spiked with albumins to concentrate using the membrane disk, anionic albumins can prevent the concentrated GNP’s from aggregation and the concentrated GNP’s remain in red color even in highly salty solutions. On the other hand without efficient protections by absorbed albumins, GNP’s aggregate and change color to blue. Using smart phone camera to acquire the concentration images of non-aggregated nanoparticles, one linear correlation is found between the red color intensity and the logarithm values of albumin concentration to quantify albumin amounts. This colorimetric assay is validated to determine the samples of the main urine protein, human serum albumin at the range of clinical significance (0.1–20 μM) in artificial urine matrix containing creatinine and urine. These results prove the feasibility of using the membrane-based micro-concentration device with mobile phone camera. [ABSTRACT FROM AUTHOR]

This paper reports using femtosecond laser marker to fabricate the three-dimensional interior microstructures in one closed flow channel of plastic substrate. Strip-like slots in the dimensions of 800 μm×400 μm×65 μm were ablated with pulse Ti:sapphire laser at 800 nm (pulse duration of ∼120 fs with 1 kHz repetition rate) on acrylic slide. After ablation, defocused beams were used to finish the surface of microstructures. Having finally polished with sonication, the laser fabricated structures are highly precise with the arithmetic roughness of 1.5 and 4.5 nm. Fabricating such highly precise microstructures cannot be accomplished with nanosecond laser marking or other mechanical drilling methods. In addition, since laser ablation can directly engrave interior microstructures in one closed chip, glue smearing problems to damage molded microstructures possibly to occur during the chip sealing procedures can be avoided too. [ABSTRACT FROM AUTHOR]

• Novel fiber optic nanoplasmonic methamphetamine biosensor based on competitive inhibition. • Superior detection limit of 0.16 ng/mL. • Short analysis time (≤15 min). • Validated by spiked urine samples. • Suitable for on-site analysis. We report the study of methamphetamine (MA) sensing in urine samples using fiber optic particle plasmon resonance (FOPPR) biosensor. This approach is intended for on-site analysis of low-molecular-weight compounds. High sensitivity detection of MA at ultra-low concentration is realized by using a competitive inhibition immunoreaction scheme based on the competition of free MA in solution for anti-MA molecules that bind to the bovine serum albumin (BSA)–MA conjugate on the gold nanoparticle surface. With the BSA–MA functionalized sensor fiber, in the presence of a fixed concentration of anti-MA and various concentrations of MA in sample, the change of transmitted light intensity through the sensor fiber relative to that in a buffer solution decreases when the MA concentration increases because of the inhibition effect of MA. Based on this sensing method, the MA-functionalized FOPPR biosensor is capable for determining the concentration of MA with high sensitivity and wide linear dynamic range of 1–1000 ng/mL. The limit of detection for MA is 0.16 ng/mL. In addition, the MA functionalized FOPPR biosensor can detect MA in diluted human urine samples without nonspecific adsorption interference. [ABSTRACT FROM AUTHOR]

Apolipoprotein E (APOE) genotyping is important for assessing the risk of late-onset Alzheimer's disease. We developed a DNA amplification-free method to perform APOE genetic analysis based on the high sensitivity of fiber optic particle plasmon resonance (FOPPR) biosensor and the specificity of ligase reaction. The method employed the dual-functional gold-iron oxide core-satellite hybrid nanoparticles (HNPs), which was modified with a single-stranded DNA (ssDNA) probe-P1, and a ssDNA probe-P2 modified with biotin to form a nanoplasmonic detection probe. Ligation of a ssDNA target complementary to the P1–P2 pair results in a ligation product with the HNP at one end and the biotin group at the other end, which can be captured by a streptavidin-functionalized sensor fiber, leading to an increase of nanoplasmonic absorption with magnitude useful for APOE genotype determination. Using synthetic ssDNA targets as standards, we achieved limits of detection in the range of 16–38 fM and the sensor responses from the mimic homozygous samples were about two times of that from mimic heterozygous samples at the same ssDNA concentration. For proof-of-principle, three genomic samples extracted from blood were analyzed and the results favorably agree with that by DNA sequencing. • Amplification-free biosensor for genotyping of Apolipoprotein E (APOE) using ligase reaction for specificity. • High sensitivity with detection limits in the range of 16–38 fM. • Allow discrimination between homozygous DNA and heterozygous DNA. • Good correlation with DNA sequencing for genomic samples extracted from blood. • Require very small amount of sample and thus provide an opportunity to develop a POCT device for APOE genotyping. [ABSTRACT FROM AUTHOR]

A new biosensing method is presented to detect gene mutation by integrating the MutS protein from bacteria with a fiber optic particle plasmon resonance (FOPPR) sensing system. In this method, the MutS protein is conjugated with gold nanoparticles (AuNPs) deposited on an optical fiber core surface. The target double-stranded DNA containing an A and C mismatched base pair in a sample can be captured by the MutS protein, causing increased absorption of green light launching into the fiber and hence a decrease in transmitted light intensity through the fiber. As the signal change is enhanced through consecutive total internal reflections along the fiber, the limit of detection for an AC mismatch heteroduplex DNA can be as low as 0.49 nM. Because a microfluidic chip is used to contain the optical fiber, the narrow channel width allows an analysis time as short as 15 min. Furthermore, the label-free and real-time nature of the FOPPR sensing system enables determination of binding affinity and kinetics between MutS and single-base mismatched DNA. The method has been validated using a heterozygous PCR sample from a patient to determine the allelic fraction. The obtained allelic fraction of 0.474 reasonably agrees with the expected allelic fraction of 0.5. Therefore, the MutS-functionalized FOPPR sensor may potentially provide a convenient quantitative tool to detect single nucleotide polymorphisms in biological samples with a short analysis time at the point-of-care sites. [ABSTRACT FROM AUTHOR]

The availability of techniques for sensitive detection of early stage osteoarthritis is critical for improving patient health. This study illustrates the feasibility of a fiber-optic particle plasmon resonance (FOPPR) sensor with gold nanoparticles on the unclad region of optical fiber probes for analysis of osteoarthritis biomarkers, tumor necrosis factor-α (TNF-α) and matrix metalloproteinases-3 (MMP-3). Results show that the sensor can achieve a refractive index resolution of 5.18 × 10−7 RIU and limits of detection for TNF-α and MMP-3 as low as 8.22 pg ml−1 (0.48 pM) and 34.3 pg ml−1 (1.56 pM), respectively. Additionally, the FOPPR sensor shows a good correlation in determining TNF-α and MMP-3 in synovial fluid with the clinically accepted enzyme-linked immunosorbent assay (ELISA) method. Finally, given the FOPPR sensor's nature of being low-cost, label-free, highly sensitive, real-time, simple-to-operate, the FOPPR sensor could offer potential to monitor biomarkers of various diseases, and provide an ideal technical tool for point-of-care diagnostics. [ABSTRACT FROM AUTHOR]

A Correction to this paper has been published: https://doi.org/10.1007/s00216-021-03353-0 [ABSTRACT FROM AUTHOR]

A rapid and ultrasensitive biosensing method based on fiber optic nanogold-linked immunosorbent assay is reported. The method employs an immobilized capture probe on the fiber core surface of an optical fiber and a detection probe conjugated to gold nanoparticles (AuNPs) in a solution. Introduction of a sample containing an analyte and the detection probe into a biosensor chip leads to the formation of a sandwich-like complex of capture probe−analyte−detection probe on the fiber core surface, through which nanoplasmonic absorption of the fiber optic evanescent wave occurs. The performance of this method has been evaluated by its application to the detection of procalcitonin (PCT), an important biomarker for sepsis. In this study, anti-PCT capture antibody is functionalized on an unclad segment of an optical fiber to yield a fiber sensor and anti-PCT detection antibody is conjugated to AuNPs to afford nanoplasmonic probes. The method provides a wide linear response range from 1 pg/mL to 100 ng/mL (5 orders) and an extremely low limit of detection of 95 fg/mL (7.3 fM) for PCT. In addition, the method shows a good correlation in determining PCT in blood plasma with the clinically validated electrochemiluninescent immunoassay. Furthermore, the method is quick (analysis time ≤15 min), requires low-cost instrumentation and sensor chips, and is also potentially applicable to the detection of many other biomarkers. • New fiber optic method using gold nanoparticle-labelled antibody and sandwich immunoassay • Superior analytical sensitivity (at fM levels). • Short analysis time (≤15 min). • Procalcitonin samples from patients validated by electrochemiluninescent immunoassay. • Suitable for point-of-care diagnostics. [ABSTRACT FROM AUTHOR]