Triple Raman Label-Encoded Gold Nanoparticle Trimers for Simultaneous Heavy Metal Ion Detection

Electrohydrodynamic-Induced SERS Immunoassay for Extensive Multiplexed Biomarker Sensing

Cancer diagnosis and patient monitoring require sensitive and simultaneous measurement of multiple cancer biomarkers considering that single biomarker analysis present inadequate information on the underlying biological transformations. Thus, development of sensitive and selective assays for multiple biomarker detection might improve clinical diagnosis and expedite the treatment process. Herein, a microfluidic platform for the rapid, sensitive, and parallel detection of multiple cancer-specific protein biomarkers from complex biological samples is presented. This approach utilizes alternating current electrohydrodynamic-induced surface shear forces that provide exquisite control over fluid flow thereby enhancing target-sensor interactions and minimizing non-specific binding. Further, the use of surface-enhanced Raman scattering-based spectral encoding with individual barcodes for different targets enables specific and simultaneous detection of captured protein biomarkers. Using this approach, the specific and sensitive detection of clinically relevant biomarkers including human epidermal growth factor receptor 2 (HER2); Mucin 1, cell surface associated (MUC1); epidermal growth factor receptor; and Mucin 16, cell surface associated (MUC16) at concentrations as low as 10 fg mL^-1 in patient serum is demonstrated. Successful target detection from patient samples further demonstrates the potential of this current approach for the clinical diagnosis, which envisages a clinical translation for a rapid and sensitive appraisal of clinical samples in cancer diagnostics.

A silica-based SERS chip for rapid and ultrasensitive detection of fluoride ions triggered by a cyclic boronate ester cleavage reaction

Chemical sensing for the convenient detection of trace aqueous fluoride ions (F^-) has been widely explored with the use of various sensing materials and techniques. It still remains a challenge to achieve ultrasensitive but simple, rapid, and inexpensive detection of F^- for environmental monitoring and protection. Here we reported a novel surface-enhanced Raman scattering (SERS) nanosensor, fluorescein phenylboronic acid covalently linked to 1,4-dimercapto-2,3-butanediol modified Au@Ag NPs by a cyclic boronate ester (Flu-PBA-Diol-Au@Ag NPs), for the rapid and ultrasensitive detection of F^-. Once the Flu-PBA approached the surface of Au@Ag NPs, the Raman signals of Flu-PBA were remarkably enhanced due to the strong SERS effect. However, the presence of F^- will induce the cleavage reaction of the cyclic boronate ester into the trifluoroborate anion (3F-Flu-PBA) and diol. The 3F-Flu-PBA molecules exfoliated from the surface of Au@Ag NPs, and the SERS signals of the nanosensor were quenched. Following the sensing mechanism, a silica-based SERS chip has been fabricated by the assembly of Flu-PBA-Diol-Au@Ag NPs on a piece of silicon wafer. The silica-based SERS chips showed high sensitivity for aqueous F^-, and the limit of detection (LOD) could reach as low as 0.1 nM. Each test using the SERS chip only needs a droplet of 20 μL sample and is accomplished within ∼10 min. The silica-based SERS chip has also been applied to the quantification of F^- in tap water and lake water.

Field and Pretreatment-Free Detection of Heavy-Metal Ions in Organic Polluted Water through an Alkyne-Coded SERS Test Kit

Field and pretreatment-free detection of heavy-metal ions in organic polluted water is important but still challenging in current water pollution emergency response systems. Here we report a polyadenine-DNA-mediated approach for a rationally designed alkyne-coded surface-enhanced Raman scattering (SERS) test kit, enabling rapid and simultaneous detection of Hg²⁺ and Ag⁺ by a portable spectrometer, impervious to organic interferences. Because of the formation of thymine (T)-Hg²⁺-T and cytosine (C)-Ag⁺-C, highly recognizable SERS signals are rapidly detected when two different alkyne-labeled gold nanoparticles (AuNPs) are induced to undergo controllable bridging upon the addition of low-volume targets. For multiplex detection through a portable spectrometer, the limits of detection reach 0.77 and 0.86 nM for Hg²⁺ and Ag⁺, respectively. Of particular significance, the proposed C≡C-containing Raman reporters provide an extremely effective solution for multiplex sensing in a spectral silent region, when the hyperspectral and fairly intense optical noises originating from lower wavenumber region (<1800 cm^-1) are inevitable under complex ambient conditions.

Embedding Raman Tags between Au Nanostar@Nanoshell for Multiplex Immunosensing

Novel Raman tags with various reporter molecules embedded in between gold nanostar (AuNS) and gold nanoshell are developed, showing significantly enhanced surface-enhanced Raman scattering intensity compared to gold nanoparticle-based composites. Immunoassay using these AuNS@tag@shell structures is highly specific with sensitivity down to 0.1 pg mL^-1 , and is capable of multiplex detection, making them highly promising for biosensing applications.

Ultrasensitive sliver nanorods array SERS sensor for mercury ions

With years of outrageous mercury emissions, there is an urgent need to develop convenient and sensitive methods for detecting mercury ions in response to increasingly serious mercury pollution in water. In the present work, a portable, ultrasensitive SERS sensor is proposed and utilized for detecting trace mercury ions in water. The SERS sensor is prepared on an excellent sliver nanorods array SERS substrate by immobilizing T-component oligonucleotide probes labeled with dye on the 3'-end and -SH on the 5'-end. The SERS sensor responses to the specific chemical bonding between thymine and mercury ions, which causes the previous flexible single strand of oligonucleotide probe changing into rigid and upright double chain structure. Such change in the structure drives the dyes far away from the excellent SERS substrate and results in a SERS signal attenuation of the dye. Therefore, by monitoring the decay of SERS signal of the dye, mercury ions in water can be detected qualitatively and quantitatively. The experimental results indicate that the proposed optimal SERS sensor owns a linear response with wide detecting range from 1pM to 1μM, and a detection limit of 0.16pM is obtained. In addition, the SERS sensor demonstrates good specificity for Hg²⁺, which can accurately identify trace mercury ions from a mixture of ten kinds of other ions. The SERS sensor has been further executed to analyze the trace mercury ions in tap water and lake water respectively, and good recovery rates are obtained for sensing both kinds of water. With its high selectivity and good portability, the ultrasensitive SERS sensor is expected to be a promising candidate for discriminating mercury ions in the fields of environmental monitoring and food safety.

Recent Progresses in Nanobiosensing for Food Safety Analysis

With increasing adulteration, food safety analysis has become an important research field. Nanomaterials-based biosensing holds great potential in designing highly sensitive and selective detection strategies necessary for food safety analysis. This review summarizes various function types of nanomaterials, the methods of functionalization of nanomaterials, and recent (2014-present) progress in the design and development of nanobiosensing for the detection of food contaminants including pathogens, toxins, pesticides, antibiotics, metal contaminants, and other analytes, which are sub-classified according to various recognition methods of each analyte. The existing shortcomings and future perspectives of the rapidly growing field of nanobiosensing addressing food safety issues are also discussed briefly.

Chiroplasmonic Assemblies of Gold Nanoparticles for Ultrasensitive Detection of 8-Hydroxy-2'-deoxyguanosine in Human Serum Sample

Gold nanoparticles (AuNPs) have been extensively explored to be used in analytical methods such as electrochemical, colorimetric methods, and so on. However, only a few methods have been reported by using chirality of AuNPs although their chiral assembly has been studied extensively and circular dichroism (CD) spectroscopy is also a simple and sensitive analytical method. In this paper, sensitive CD spectroscopy method has been explored for detection of 8-hydroxy-2'-deoxyguanosine (8-OHdG), a well-known biomarker for oxidative DNA damage, based on DNA-induced chiroplasmonic assemblies of AuNPs. First, 8-OHdG aptamer hybridized with its complementary sequence that modified with AuNPs based on precision matched bases. DNA-modified AuNPs were assembled into AuNPs dimers by 8-OHdG aptamer, which displayed strong chiroptical activity. Subsequently, in the presence of 8-OHdG, the high specific recognition and affinity constants of aptamer and 8-OHdG destroyed the hybrid of aptamer and its complementary sequence; as a result, AuNPs dimers were destroyed and showed low CD signal. The CD intensity was in log-linear correlation with the concentration of 8-OHdG ranging from 0.05 to 2 nM, with a correlation coefficient of 0.9951 and a detection limit of 33 pM (S/N = 3). The method has been successfully applied in a complex matrix such as human serum samples. The recoveries were from 92.5% to 107% and the relative standard derivations were in the range of 4.89% ∼ 7.27%, indicating that the method had good accuracy and high precision. Therefore, these results indicated that the proposed CD method was simple and reliable, which held great potential for clinical examinations.

Bioinspired Synthesis of All-in-One Organic-Inorganic Hybrid Nanoflowers Combined with a Handheld pH Meter for On-Site Detection of Food Pathogen

With a mild elaborately bioinspired one-pot process, Con A-GOx-CaHPO4 nanoflowers are prepared. Employing the as-prepared all-in-one hybrid nanoflowers as signal tags, a simple but potentially powerful amplification biosensing technology for the detection of food pathogen with excellent simplicity, portability, sensitivity, and adaptability is achieved.

Highly Sensitive and Selective In-Situ SERS Detection of Pb(2+), Hg(2+), and Cd(2+) Using Nanoporous Membrane Functionalized with CNTs

Porous Anodic Alumina (PAA) membrane was functionalized with CoFe₂O₄ nanoparticles and used as a substrate for the growing of very long helical-structured Carbon Nanotubes (CNTs) with a diameter less than 20 nm. The structures and morphologies of the fabricated nanostructures were characterized by field emission- scanning electron microscopy (FE-SEM), energy dispersive X-ray (EDX), and Raman spectroscopy. By uploading the CNTs on PAA, the characteristic Raman peaks of CNTs and PAA showed 4 and 3 times enhancement, respectively, which leads to more sensitive Surface-Enhanced Raman Spectroscopy (SERS) substrates. For comparison, PAA and CNTs/PAA arrays were used as SERS substrates for the detection of Hg²⁺, Cd²⁺, and Pb²⁺. The proposed sensor demonstrated high sensitivity and selectivity between these heavy metal ions. CNTs/PAA sensor showed excellent selectivity toward Pb²⁺ over other metal ions, where the enhancement factor is decreased from ~17 for Pb²⁺ to ~12 for Hg²⁺ and to ~4 for Cd²⁺. Therefore, the proposed CNTs/PAA sensor can be used as a powerful tool for the determination of heavy metal ions in aqueous solutions.

A SERS-active sensor based on heterogeneous gold nanostar core-silver nanoparticle satellite assemblies for ultrasensitive detection of aflatoxinB1

A surface-enhanced Raman scattering (SERS) sensor based on gold nanostar (Au NS) core-silver nanoparticle (Ag NP) satellites was fabricated for the first time to detect aflatoxinB1 (AFB1). We constructed the SERS sensor using AFB1 aptamer (DNA1)-modified Ag satellites and a complementary sequence (DNA2)-modified Au NS core. The Raman label (ATP) was modified on the surface of Ag satellites. The SERS signal was enhanced when the satellite NP was attached to the Au core NS. The AFB1 aptamer on the surface of Ag satellites would bind to the targets when AFB1 was present in the system, Ag satellites were then removed and the SERS signal decreased. This SERS sensor showed superior specificity for AFB1 and the linear detection range was from 1 to 1000 pg mL(-1) with the limit of detection (LOD) of 0.48 pg mL(-1). The excellent recovery experiment using peanut milk demonstrated that the sensor could be applied in food and environmental detection.

Mercury species induced frequency-shift of molecular orientational transformation based on SERS

We proposed a novel readout method based on a peculiar phenomenon in which the vibrational frequencies of a SERS-active probe (dimethyldithiocarbamic acid sodium salt, DASS) can be affected when there is mercury species.

Development of a mitochondria-targeted fluorescent probe for hydrazine monitoring in living cells

A novel mitochondria-targeted fluorescent probe was presented, which could image exogenous hydrazine in living cells.

Facile synthesis of multi-responsive functional graphene quantum dots for sensing metal cations

Aminated and phosphorylated graphene quantum dots (PiNGQDs) have been synthesized and used as fluorescent probes for sensing metal cations.

Double Detection of Mycotoxins Based on SERS Labels Embedded Ag@Au Core-Shell Nanoparticles

A sensitive surface-enhanced Raman scattering (SERS) signal dependent double detection of mycotoxins is achieved for the first time, without the aid of nucleic acid amplification strategies. SERS labels embedded Ag@Au core-shell (CS) nanoparticles (NPs) as novel SERS tags are successfully prepared through a galvanic replacement-free deposition. SERS tags produce stable and quantitative SERS signal, emerging from the plasmonic coupling at the junction of Ag core and Au shell. SERS tags engineered Raman aptasensors are developed for the double detection of ochratoxin A (OTA) and aflatoxin B1 (AFB1) in maize meal. The limits of detection (LODs) are as low as 0.006 ng/mL for OTA and 0.03 ng/mL for AFB1. The developed protocol can be extended to a large set of different SERS tags for the sensitive detection of multiple targets that possess different lengths of aptamers.

SERS-active silver nanoparticle trimers for sub-attomolar detection of alpha fetoprotein

SERS-active silver nanoparticle trimers were assembled in this study for the first time, through the aptamer of a cancer biomarker, alpha fetoprotein (AFP).

A SERS active bimetallic core–satellite nanostructure for the ultrasensitive detection of Mucin-1

In this study, we established gold nanorods (Au NRs) core–silver nanoparticles (Ag NPs) satellite assemblies as an ultrasensitive aptamer-based SERS sensor for the detection of Mucin-1, a specific breast cancer marker protein.

SERS-active Au NR oligomer sensor for ultrasensitive detection of mercury ions

In this study, we developed a sensitive surface-enhanced Raman scattering (SERS) sensor based on a self-assembled Au NR oligomer for the detection of mercury ions (Hg²⁺) in aqueous solution.