Bf-miRNAs Isolation
Here are most widely used commercial Bf-miRNA isolation kits and related papers

miRNeasy Serum/Plasma Kit -From Qiagen

This kit has been specially designed Bi-miRNA isolation. Biofluids like blood, serum and urine can be used for miRNAs isolation. The miRNeasy Serum/Plasma Kit is designed for purification of cell-free total RNA — primarily miRNA and other small RNA — from small volumes of serum and plasma. RNA from serum and plasma typically consists of molecules <100 nucleotides. The miRNeasy Serum/Plasma Kit includes a miScript Primer Assay that detects the miRNeasy Serum/Plasma Spike-In Control, providing a convenient system for normalization. The miRNeasy Serum/Plasma Spike-In Control (ordered separately) is a C. elegans miR-39 miRNA mimic and is supplied lyophilized at 10 pmol per tube.
https://www.qiagen.com/us/products/catalog/sample-technologies/rna-sample-technologies/mirna/mirneasy-serumplasma-kit/

 mirVana™ miRNA Isolation Kit-From Life technologies

Although this kit has been designed for miRNAs isolation from tissues and cells, several researchers used this kit for the isolate of  miRNAs from biofluids such as blood/serum/plasma and urine. The mirVana™ miRNA Isolation Kit combines the advantages of organic extraction and solid-phase extraction.

https://www.lifetechnologies.com/order/catalog/product/AM1560

 miRCURY™ RNA Isolation Kits -From Exiqon

Column-based RNA isolation kit specifically for biofluids, including serum/plasma, urine and CSF.  Fully compatible with the miRCURY LNA™ Universal RT microRNA PCR system for highly sensitive detection of microRNA.

http://www.exiqon.com/mirna-isolation-biofluids

 Enhanced extraction efficiency of miRNA from cells by addition of Triton X-100
The determination of microRNA (miRNA) levels in biomaterials has become important for understanding their biological functions and for the diagnosis of various diseases. An effective extraction method is needed for maximizing the recovery of miRNAs from cells, while minimizing RNA degradation during the extraction because miRNAs present only approximately 0.01 % of total RNA. In this study, we used Triton X-100 (TX-100) to improve the extraction efficiency of miRNAs with TRIzol® reagent, which is a commonly used commercial microRNA isolation kit. The concentration of TX-100 and the incubation time after the addition of TX-100 were optimized to maximize the extraction efficiency. The extraction recovery by a combination of TX-100 and TRIzol® reagent was approximately 1.9-fold greater than that by the TRIzol® reagent alone. We have established a very effective extraction method for the extraction of low-abundance miRNAs in biological samples for the determination of miRNA levels in biomaterials.

http://link.springer.com/article/10.1007/s00216-013-7170-0