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Abstract: A fabrication of a novel simple porous silicon polybasic photonic crystal with symmetrical structure has been reported as a nucleic acid biosensor for detecting antifreeze protein gene in insects (Microdera puntipennis dzhungarica), which would be helpful in the development of some new transgenic plants with tolerance of freezing stress. Compared to various porous silicon-based photonic configurations, porous silicon polytype layered structure is quite easy to prepare and shows more stability; moreover, polybasic photonic crystals with symmetrical structure exhibit interesting optical properties with a sharp resonance in the reflectance spectrum, giving a higher Q factor which causes higher sensitivity for sensing performance. In this experiment, DNA oligonucleotides were immobilized into the porous silicon pores using a standard crosslink chemistry method. The porous silicon polybasic symmetrical structure sensor possesses high specificity in performing controlled experiments with non-complementary DNA. The detection limit was found to be 21.3nM for DNA oligonucleotides. The fabricated multilayered porous silicon-based DNA biosensor has potential commercial applications in clinical chemistry for determination of an antifreeze protein gene or other genes. [Copyright &y& Elsevier]

Abstract: External random factors have a great influence on the fabrication of accurate photonic crystal, especially porous silicon-based photonic crystals. Compared with the binary photonic crystal, polybasic structure photonic crystal shows more stability and smaller effect of the random fluctuation. In this paper, we have fabricated a novel simple porous silicon polybasic Bragg''s mirror combined with excellent specific antigen–antibody inmunoreaction as an immunosensor for determining Hydroxysafflor yellow A (HSYA), which is the main chemical component of Carthamus tinctorius L. The binding of HSYA and the polyclonal anti-HSYA antibodies causes red shifts in the reflection spectrum of the sensor, and the red shift was proportional to the HSYA concentration with linear relationship ranging from 1 to 3μgmL−1 with a detection limit of 0.78ngmL−1. Importantly, this research offers hope for development of a commercial porous silicon-based immunosensor for component determination of C. tinctorius L. or other antigens. [Copyright &y& Elsevier]

Gold nanoparticles/785 porous silicon photonic crystals (Au NPs/785 PSi PhCs) were used as substrates in combination with a low-concentration serum surface-enhanced Raman spectroscopy (SERS) detection scheme to obtain spectral signals from healthy individuals and cervical cancer patients. The best principal component scores were selected by principal component analysis (PCA) combined with linear discriminant analysis (LDA) and support vector machine (SVM) to analyze the spectral differences distinguishing healthy and cervical cancer patients. The accuracy of the two models was 97.9% and 96.9%, respectively. SERS technique based on Au NPs/785 PSi PhCs has great potential to improve the screening of cervical cancer. [ABSTRACT FROM AUTHOR]

To improve the detection sensitivity of a porous silicon optical biosensor in the real-time detection of biomolecules, a non-spectral porous silicon optical biosensor technology, based on dual-signal light detection, is proposed. Double-light detection is a combination of refractive index change detection and fluorescence change detection. It uses quantum dots to label probe molecules to detect target molecules. In the double-signal-light detection method, the first detection-signal light is the detection light that is reflected from the surface of the porous silicon Bragg mirror. The wavelength of the detection light is the same as the wavelength of the photonic band gap edge of the porous silicon Bragg mirror. CdSe/ZnS quantum dots are used to label the probe DNA and hybridize it with the target DNA molecules in the pores of porous silicon to improve its effective refractive index and enhance the detection-reflection light. The second detection-signal light is fluorescence, which is generated by the quantum dots in the reactant that are excited by light of a certain wavelength. The Bragg mirror structure further enhances the fluorescence signal. A digital microscope is used to simultaneously receive the digital image of two kinds of signal light superimposed on the surface of porous silicon, and the corresponding algorithm is used to calculate the change in the average grey value before and after the hybridization reaction to calculate the concentration of the DNA molecules. The detection limit of the DNA molecules was 0.42 pM. This method can not only detect target DNA by hybridization, but also detect antigen by immune reaction or parallel biochip detection for a porous silicon biosensor. [ABSTRACT FROM AUTHOR]

A technique is demonstrated to detect DNA hybridization based on surface layer of Au/porous silicon microcavity (Au/PSM) substrate for very small amount of biomolecules. Simulations show that the increase of effective refractive index for the first layer of PSM will cause a blue shift for its reflectance spectrum, and the blue shift becomes less with the increase of refractive index for one more layers. In experiments, such a blue shift of reflectance spectrum of PSM comes from the increase of refractive index by DNA hybridization on the surface. The detection limit of Au/PSM biosensor is 15.15 nM for 19-base pair DNA, which is comparable to that of reported biosensors based on porous silicon (PS). Therefore such an Au/PSM could be very useful to develop simple, rapid and sensitive optical biosensors when the amount of target is very small. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sensitive and reproducible CuNPs@AgNPs@PSB SERS substrates were prepared using a self-assembly approach. • The CuNPs@AgNPs structure was successfully synthesized on the Porous silicon Bragg reflector (PSB) surface using the reduction of PSB and copper nanoparticles. • Low concentration detection of R6G and CPPU was completed. • The prepared high-performance and high-sensitivity SERS substrate have a very promising application in detection technology. The development of a highly sensitive, synthetically simple and economical SERS substrate is technically very important. A fast, economical, sensitive and reproducible CuNPs@AgNPs@ Porous silicon Bragg reflector (PSB) SERS substrate was prepared by electrochemical etching and in situ reduction method. The developed CuNPs@AgNPs@PSB has a large specific surface area and abundant "hot spot" region, which makes the SERS performance excellent. Meanwhile, the successful synthesis of CuNPs@AgNPs can not only modulate the plasmon resonance properties of nanoparticles, but also effectively prolong the time stability of Cu nanoparticles. The basic performance of the substrate was evaluated using rhodamine 6G (R6G). (Detection limit reached 10−15 M, R2 = 0.9882, RSD = 5.3 %) The detection limit of Forchlorfenuron was 10 μg/L. The standard curve with a regression coefficient of 0.979 was established in the low concentration range of 10 μg/L −100 μg/L. This indicates that the prepared substrates can accomplish the detection of pesticide residues in the low concentration range. The prepared high-performance and high-sensitivity SERS substrate have a very promising application in detection technology. [ABSTRACT FROM AUTHOR]

The influence of permeable layer number of porous silicon microcavity (PSM) on the reflectance spectrum has been carried out from both simulations and experiments. The increase of the effective refractive index of the first porous silicon (PS) layer of PSM will causes a blue shift for the reflectance spectrum. With one more layer refractive index increasing, the blue shift becomes less, and it will shift to a higher wavelength when the layer number becomes large enough. This study would be helpful for simple fabrication of highly sensitive, fast responsible biosensors based on the blue shift of reflectance spectrum, and such fabricated Au/PSM substrate of multilayer PS might have a potential to detect minor biomolecules by means of surface state effects. [ABSTRACT FROM AUTHOR]

We report on the fluorescence enhancement induced by gold nanoparticles (Au NPs) deposited on porous silicon Bragg reflectors (Bragg PS). The rhodamine 6 G (R6G) fluorescence was studied on single-layer porous silicon films and porous silicon Bragg reflectors. By comparison, R6G fluorescence of porous silicon films with Au NPs infiltrated is about two times that of porous silicon films without Au NPs. The R6G fluorescence of this porous silicon Bragg reflectors with Au NPs infiltrated is also stronger than the single-layered porous silicon films (∼2.3-fold) with Au NPs infiltrated. Such substrates with a multiple enhancement of the fluorescence have great potential for applications in the fields of medical diagnostics and biotechnology. [ABSTRACT FROM AUTHOR]

We fabricated a new porous silicon photonic device which is a special multi-layer porous silicon including two different single layer porous silicon and a porous silicon Bragg mirror, and investigated the influence of porous silicon Bragg mirror's structure on the fluorescence intensity of quantum dots (QDs) which infiltrated into porous silicon device, and CdSe/ZnS QDs we used emit at 605 nm and 625 nm respectively. By immersing porous silicon samples in QDs solution, QDs were successfully infiltrated into porous silicon devices which have high reflection band at or beyond fluorescence peak. Experimental results show that the fluorescence intensity of QDs which infiltrated into the first layer of porous silicon device can be enhanced when fluorescence peak falls into the high reflection band of porous silicon device. [ABSTRACT FROM AUTHOR]

Abstract: With optimized parameters and the optimized sequence structure from simulations, proper porous silicon microcavity (PSM) based on silicon-on-insulator (SOI) wafer, constituted of a Fabry–Perot cavity between distributed Bragg reflectors (DBRs), has been achieved. Just as expected, the resonance wavelengths of these two oxidized PSMs are located separately at 1328nm and 1560nm, which are very close to the optical communication wavelengths of 1310nm and 1550nm. The effects of tuning resonance wavelength were shown by composition of Fabry–Perot cavity integrated on each thickness of porous silicon layer. Since the preparation technology of optical devices with these working wavelengths has been well developed, it is expected that such a design could be of great potential in realizing integrated optical devices. Compared with various optical devices on SOI wafer, PSM based on SOI by electrochemical anodization is simple and low-cost. Moreover, a sharp resonance in the reflectance spectrum means a high Q factor which predicts an interesting possibility in sensor application on SOI wafer. [Copyright &y& Elsevier]

Abstract: A novel method is demonstrated to detect Antifreeze proteins (AFPs) based on photoluminescence (PL) using porous silicon (PS) coated with silver as a substrate. Ag/PS substrate is obtained through immersion of PS in silver nitrate (AgNO3) solutions and is incubated with Rhodamine B (RB) as PL label. This substrate is easy to be fabricated and the pore size of PS is large enough for biological molecules to infiltrate, which is an ideal platform for biological molecule detection. Through functionalization used glutaraldehyde (GTA) and 4-(N-Maleimidomethyl) cyclohexane-1-carboxylicacid (Sulfo-SMCC) as cross-linkers separately, we test the role of the AFPs antibodies in selective capturing the AFPs antigen and explain the reason of the enhancement of PL intensity. The result shows a significant enhancement of the PL intensity of RB at around 590 nm due to the interaction of antibody–antigen competitive binding with AFPs. Therefore, the PL corresponding to RB was selected to detect the target AFPs and the PL intensity of RB proportional to the AFPs concentration. The detection limit was found to be 1.65 μg/ml for AFPs when GTA was used as cross-linker, and the detection limit was 16.5 ng/ml with Sulfo-SMCC as cross-linker. [Copyright &y& Elsevier]

[Display omitted] • Nanoparticles are uniformly embedded in PSi chips with 40–60 nm pore size, enhancing BRC serum signal. • The Ag 2 O-Ag core–shell structure effectively prevents silver from being oxidized by sulfur, giving the chip a shelf life of six months. • The PCA-t-SNE rapid screening model combined with the SERS microarray provides the basis for the development of a low-cost, rapid and sensitive technique for early screening of breast cancer. Ag 2 O-Ag-PSi (porous silicon) surface-enhanced Raman scattering (SERS) chip was successfully synthesized by electrochemical corrosion, in situ reduction and heat treatment technology. The influence of different heat treatment temperature on SERS performance of the chip is studied. The results show that the chip treated at 300 °C has the best SERS performance. The chip was composed of Ag 2 O-Ag nano core shell with a diameter of 40–60 nm and porous silicon substrate. Then, the optimized chip was used to perform SERS test on serum samples from 30 healthy volunteers and 30 early breast cancer patients, and the baseline was corrected by LabSpec6 software. Finally, the data were analyzed by principal component analysis combined with t-distributed Stochastic Neighbor Embedding (PCA-t-SNE). The results showed that the accuracy of the improved substrate combined with multivariate statistical method was 98%. The shelf life of the chips exceeded six months due to the presence of the Ag 2 O shell. This study provides a basis for developing a low-cost rapid and sensitive early screening technology for breast cancer. [ABSTRACT FROM AUTHOR]

To improve the detection sensitivity of porous silicon microcavity biosensors, CdSe/ZnS quantum dots are used to label complementary DNA molecules for the refractive index amplification and angular spectrum method for detection. In this method, the TE mode laser is used as the detection light and the light source is changed into a parallel beam by collimating and expanding the beam, which illuminates the PSM surface and receives the reflected light from the PSM surface through the detector. The angle corresponding to the weakest reflected light intensity before and after the biological reaction between probe DNA and complementary DNA of different concentrations labeled by quantum dots was measured by the detector, and the relationship between the angle change before and after the biological reaction and the complementary DNA concentration labeled by quantum dots was obtained. The experimental results show that the angle change increases linearly with increasing complementary DNA concentration. The detection limit of the experiment, as determined by fitting, is approximately 36 pM. The detection limit of this method is approximately 1/300 of that without quantum dot labeling. Our method has a low cost because it does not require the use of a reflectance spectrometer, and it also demonstrates high sensitivity. [ABSTRACT FROM AUTHOR]

Ag 2 O–Ag-porous silicon Bragg mirror (PSB) composite SERS substrates were successfully synthesized by using a combination of electrochemical and thermochemical methods. Test results showed that the SERS signal increased and decreased as the annealing temperature used for the substrate increased, where the most intense SERS signal was obtained using a substrate annealed at 300 °C. Stability test results showed substantial enhancement of the SERS signal intensity of the Ag 2 O-Ag-PSB composite one month after preparation compared with that of conventional Ag-PSB. We conclude that Ag 2 O nanoshells play an essential role in SERS signal enhancement. Ag 2 O prevents natural oxidation of Ag nanoparticles (AgNPs) and has a solid localized surface plasmon resonance (LSPR). SERS signal enhancement was tested using this substrate for serum from patients with Sjögren's syndrome (SS) and Diabetic nephropathy (DN), as well as from healthy controls (HC). SERS feature extraction was performed using principal component analysis (PCA). The extracted features were analyzed by a support vector machine (SVM) algorithm. Finally, a rapid screening model for SS and HC, as well as DN and HC, was developed and used to perform controlled experiments. The results showed that the diagnostic accuracy, sensitivity and selectivity for SERS technology combined with machine learning algorithms reached 90.7%, 93.4% and 86.7% for SS/HC and 89.3%, 95.6% and 80% for DN/HC, respectively. The results of this study show that the composite substrate has excellent potential to be developed into a commercially available SERS chip for medical testing. [Display omitted] • The optimized morphology of AgNPs and the excellent optical properties of PSB were combined to amplify the serum SERS signal. • The stability of the substrate is twofold: stability to serum samples and stability under different storage cycles. • Analytical modeling of SERS serum spectra using PCA-LDA produced excellent results on both chronic disease datasets. [ABSTRACT FROM AUTHOR]

In this work, a new dual signal light detection method based on porous silicon Bragg mirror (PSBM) and biological labelling with quantum dots (QDs) is proposed for the detection of beta-lactoglobulin (β-lg). The first signal light is a probe light emitted by a laser with wavelength of 633 nm, which enters the PSBM and is reflected from the surface. The wavelength of the probe light is located at the edge of the PSBM band gap, where it has the lowest reflectivity. β-lg antibodies is labelled with CdSe/ZnS QDs and reacts with β-lg molecules have been fixed to the inner wall of the porous silicon pores. Due to the specific binding of biomolecules in PSBM, the refractive index of the device increases, resulting in the enhancement of detection reflected light. The QDs play the role of refractive index amplification. The second signal light is the fluorescence of QDs in immune reactants. QDs produce fluorescence at 630 nm when excited by a short-wavelength laser. The fluorescence signal is further enhanced by PSBM. The superimposed images of two kinds of light on the surface of PSBM are obtained by digital microscope at the same time. By calculating the average grey value change of the image before and after biological reaction, β-lg can be detected with high sensitivity. The detection limit of β-lg was 0.12 ng/mL. The experimental results showed that the PSBM-based dual signal light method could be used to detect the content of cow milk adulterated in β-lg free camel milk. • The wavelengths of both probe light and fluorescence are selected at the band gap edge of porous silicon with Bragg structure. • The two changes of fluorescence and refractive index of the sensor before and after biological reaction are used to detect the target biomolecules. • Quantum dots play two roles in detection, one is to generate fluorescence after excitation and another is to achieve refractive index amplification. • Biological detection is implemented by the average grey value change of the images before and after biological reaction. • Proposed method can be applied to detect β-lactoglobulin. [ABSTRACT FROM AUTHOR]

• High-performance Au NPs/PSi was successfully fabricated on a large-scale. • With the advantages of MIL, the MIL-Au NPs /PSi active substrate with strong adsorption property was prepared. • MIL-Au NPs/PSi exhibits excellent sensitivity and stability in the detection for probe molecule. • A novel method for the detection of arsenite was proposed, with the detection limit as low as 0.5 ppb. Developing a novel and simple route for the synthesis ultrasensitive and specific SERS substrates is highly desirable and technically important. Here, a magnetic ionic liquid (MIL) assisted strategy is developed, and the high-quality and ultra-sensitive MIL-gold nanoparticles/porous silicon (MIL-Au NPs/PSi) composite substrate were synthesized by a fast and cost effective strategy with the assistance of MIL (1-methyl-3-hexyl imidazole ferric tetrachloride ([C 6 mim]FeCl 4). Fundamental SERS performance of this composite substrate was evaluated using rhodamine 6G (R6G). The results showed that MIL make the Au NPs/PSi have great advantages in synergetic enhancement and stability, and the hypersensitive detection of specific substances can be realized by selecting or designing IL. Based on the particularity of MIL ([C 6 mim] FeCl 4 ′s function and structure, arsenic was detected with MIL-Au NPs/PSi substrate. The detection limit can reach 0.5 ppb, and the standard curves with regression coefficients of 0.98527 and 0.98965 were established in the linear range of 2–80 ppb and 200–800 ppb. In a word, an advanced method for the preparation of high-performance and designable SERS substrate has been developed, which will certainly show promising applications in detection technology. [ABSTRACT FROM AUTHOR]

Uniform, low-cost, surface-enhanced Raman scattering (SERS) active substrates were prepared by sputtering silver onto porous silicon (pSi) fabricated by an electrochemical etching method. The resulting Ag/pSi SERS substrates were characterized by scanning electron microscopy (SEM), and the SERS effect of the substrates was investigated using rhodamine 6G (R6G) as a probe. Furthermore, the signal uniformity of the Ag/pSi SERS substrates was confirmed through mapping measurements. The Ag/pSi SERS substrates exhibited uniform shape and size and stable SERS activity. Then, we demonstrated the capacity of the prepared silicon-based SERS substrates for detecting bovine serum albumin (BSA) and serum samples. Therefore, our Ag/pSi SERS substrates can be easily employed in practical applications to effectively assess healthcare. [ABSTRACT FROM AUTHOR]